System and method for SRS switching, transmission, and enhancements

ABSTRACT

User Equipments (UEs) may be assigned a set of aggregated component carriers for downlink carrier aggregation and/or carrier selection. Some UEs may be incapable of transmitting uplink signals over all component carriers in their assigned set of aggregated component carriers. In such scenarios, a UE may need to perform SRS switching in order to transmit SRS symbols over all of the component carriers. Embodiments of this disclosure provide various techniques for facilitating SRS switching. For example, a radio resource control (RRC) message may be used to signal a periodic SRS configuration parameter. As another example, a downlink control indication (DCI) message may be used to signal an aperiodic SRS configuration parameter. Many other examples are also provided.

This application is a continuation of U.S. patent application Ser. No.16/053,542, filed on Aug. 2, 2018 and entitled “System and Method forSRS Switching, Transmission, and Enhancements”, which is a continuationof U.S. patent application Ser. No. 15/477,639, filed on Apr. 3, 2017and entitled “System and Method for SRS Switching, Transmission, andEnhancements,” (now U.S. patent Ser. No. 10/270,570, issued on Apr. 23,2019) which is a continuation of International Application No.PCT/US17/25577 filed on Mar. 31, 2017, and claims priority to U.S.Provisional Application No. 62/317,327 filed on Apr. 1, 2016, U.S.Provisional Application No. 62/317,351 filed on Apr. 1, 2016, U.S.Provisional Application No. 62/336,347 filed on May 13, 2016, U.S.Provisional Application No. 62/374,527 filed on Aug. 12, 2016, U.S.Provisional Application No. 62/378,030 filed on Aug. 22, 2016, and U.S.Provisional Application No. 62/401,701 filed on Sep. 29, 2016, each ofwhich is hereby incorporated by reference herein as if reproduced in itsentirety.

TECHNICAL FIELD

The present invention relates to a system and method for wirelesscommunications, and, in particular embodiments, to a system and methodfor sounding reference signal switching.

BACKGROUND

Next-generation wireless networks will need to provide higher throughputto support greater numbers of subscribers as well as applicationsrequiring high-data rates, such as video, high-definition images, andthe like. Various techniques have been proposed to increase the overallthroughput provided to mobile devices in a wireless network. One suchtechnique is carrier aggregation, which communicates data to, or from, amobile device over multiple carriers at the same time, therebyincreasing the bandwidth available to the mobile device. Anothertechnique is carrier selection (also referred to as carrier switching),where an existing communications session associated with a mobile deviceis switched from one carrier to another. Carrier selection may increasethe effective bandwidth available to a mobile device by allowing thecommunications session to be transitioned over to a component carrierthat is exhibiting better channel quality.

SUMMARY

Technical advantages are generally achieved, by embodiments of thisdisclosure which describe systems and methods for SRS Switching,Transmission, and Enhancements.

In accordance with an embodiment, a method for reference signaltransmission is provided. In this example, the method includes receivingone or more downlink transmissions over a first set of aggregatedcomponent carriers is provided. The UE is capable of transmitting uplinksignals over fewer than all component carriers in the first set ofaggregated component carriers at the same time. The method furtherincludes transmitting sounding reference signal (SRS) symbols overdifferent component carriers in the first set of aggregated componentcarriers during different time periods. An apparatus for performing thismethod is also provided.

In accordance with another embodiment, a method for reference signalreception is provided. In this example, the method includes transmittingone or more downlink signals to a user equipment (UE) over a first setof aggregated component carriers. The UE is incapable of transmittinguplink signals over all component carriers in the first set ofaggregated component carriers at the same time. The method furtherincludes receiving sounding reference signal (SRS) symbols from the UEover different component carriers in a first set of aggregated componentcarriers during different time periods. An apparatus for performing thismethod is also provided.

In accordance with another embodiment, a method for transmitting uplinksignals is provided. In this example, the method includes transmitting afirst uplink signal in a first subframe over a first component carrierduring a first period. The first uplink signal carrying at least a firstsounding reference signal (SRS) symbol. The method further includesswitching from the first component carrier to a second component carrieraccording to an SRS switching schedule. An uplink RF retuning delay isassociated with switching from the first component carrier to the secondcomponent carrier. The method further includes transmitting a seconduplink signal in a second subframe over the second component carrierduring a second period. The second uplink signal carries at least one ofa second SRS symbol and a random access preamble.

In accordance with another embodiment, a method for reference signalswitching is provided. In this example, the method includes transmittinga first sounding reference signal (SRS) symbol over a primary componentcarrier during a first period. The UE that transmitted the SRS symbol isscheduled to transmit both a second SRS symbol over a secondarycomponent carrier during a second period and an uplink control messageover the primary carrier during the second period. This creates ascheduling conflict between the SRS symbol and the uplink controlmessage. The method further includes transmitting the uplink controlmessage over the primary component carrier during the second periodwithout transmitting the second SRS symbol over the secondary componentcarrier during the second period when the uplink control messagesatisfies a criterion.

In accordance with another embodiment, a method for transmitting uplinksignals is provided. In this example, the method includes receiving acontrol signal from a base station that indicates that a set ofaggregated component carriers are assigned to a timing advance group(TAG). At least a first component carrier assigned to the TAG does notsupport physical uplink control channel (PUCCH) signaling or physicaluplink shared channel (PUSCH) signaling. The method further includestransmitting a sounding reference signal (SRS) symbol over one or morecomponent carriers assigned to the TAG according to a timing advanceparameter associated with the TAG.

In accordance with another embodiment, a method for receiving uplinksignals is provided. In this example, the method includes transmitting adownlink signal to a UE over a set of aggregated component carriers,receiving a first sounding reference signal (SRS) symbol from the UEover a first component carrier in the set of aggregated componentcarriers during a first period, and receiving a second SRS symbol fromthe UE over a second component carrier in the set of aggregatedcomponent carriers during a second period. The second component carrieris different than the first component carrier.

In accordance with another embodiment, a method for transmitting controlsignals is provided. In this example, the method includes transmitting acontrol signal to a UE. The control signal indicates that a set ofaggregated component carriers are assigned to a timing advance group(TAG). At least one component carrier assigned to the TAG does notsupport physical uplink control channel (PUCCH) signaling and physicaluplink shared channel (PUSCH) signaling, and the control signal promptsthe UE to transmit a sounding reference signal (SRS) symbol over one ormore component carriers assigned to the TAG according to a timingadvance parameter associated with the TAG.

In accordance with another embodiment, a method for receiving uplinksignals is provided. In this example, the method includes receiving arandom access channel (RACH) transmission from a user equipment (UE).The RACH transmission requests a timing advance for a component carrierwithout requesting a grant for physical uplink control channel (PUCCH)resource and without requesting a grant for physical uplink sharedchannel (PUSCH) resources. The method further includes transmitting acontrol signal to the UE that indicates the timing advance for thecomponent carrier, and receiving one or more sounding reference signal(SRS) symbols from the UE over the component carrier in accordance withthe timing advance without receiving any PUSCH signaling over thecomponent carrier and without receiving any PUCCH signaling over thecomponent carrier.

In accordance with another embodiment, a method for reference signaltransmission is provided in this example, the method includes reportinga component carrier capability of a user equipment (UE) to a basestation, configuring the UE based on information from the base station,a first set of component carriers for one or more downlink reception,configuring the UE based on information from the base station a firstsubset of component carriers, in the first set of component carriers,for one or more uplink transmissions. The one or more transmissionsinclude at least one of physical uplink control channel (PUCCH),physical uplink shared channel (PUSCH), or sounding reference signal(SRS) symbol transmissions. The UE is capable of transmitting uplinksignals over all component carriers in the first subset of componentcarriers at the same time. The method further includes configuring theUE based on information from the eNB, a second subset of componentcarriers, in the first set of component carriers, for one or more SRStransmissions without configured the second subset of component carriersfor PUSCH/PUCCH transmissions, and transmitting SRS symbols overdifferent component carriers in the first subset of component carriersand second subset of component carriers during different time periods.

In accordance with another embodiment, a method for reference signaltransmission is provided. In this example, the method includestransmitting a first uplink signal over a first component carrier duringa first period. The first uplink signal carries at least a firstsounding reference signal (SRS) symbol. The method further includesswitching from the first component carrier to a second component carrieraccording to a switching parameter for an SRS switching schedule, andtransmitting a second uplink signal over the second component carrierduring a second period. The second uplink signal carrying at least oneof a second SRS symbol and a random access preamble, wherein thetransmission occurs after an uplink RF retuning time.

In accordance with another embodiment, a method for reference signaltransmission is provided. The method comprises receiving one or moredownlink transmissions over a set of aggregated component carriers, andtransmitting at least one of a first sounding reference signal (SRS)symbol, and at least one of physical uplink shared channel (PUSCH)signal and physical uplink control channel (PUCCH) signaling over afirst component carrier in the set of aggregated component carriersduring a first period. At least one of the parameters for the SRS symbolis generated based on a parameter for the PUSCH. The method furtherincludes transmitting at least a second SRS symbol over a secondcomponent carrier in the set of aggregated component carriers during asecond period without transmitting any PUSCH signal and PUCCH signalingover the second component carrier during the second period. The secondcomponent carrier being different than the first component carrier, andnone of the parameters for the SRS symbol is generated based on aparameter for any PUSCH.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawing, in which:

FIG. 1 is a diagram of an embodiment wireless communications network;

FIG. 2 is a diagram of a network for supporting SRS switching;

FIG. 3 is a diagram of an embodiment communications sequence forconfiguring a periodic SRS switching schedule;

FIG. 4 is a flowchart of an embodiment method for transmitting SRSsymbols;

FIG. 5 is a flowchart of an embodiment method for performing channelestimation based on SRS symbols;

FIG. 6 is a diagram of an embodiment communications sequence forconfiguring, or otherwise triggering, an aperiodic SRS symboltransmission;

FIG. 7 is a flowchart of another embodiment method for transmitting SRSsymbols;

FIG. 8 is a flowchart of another embodiment method for performingchannel estimation based on SRS symbols;

FIG. 9 is a diagram of an embodiment communications sequence forconfiguring a DCI message format associated with an SRS configurationparameter;

FIG. 10 is a flowchart of yet another embodiment method for transmittingSRS symbols;

FIG. 11 is a flowchart of a yet another embodiment method for performingchannel estimation based on SRS symbols;

FIG. 12 is a diagram of an embodiment communications sequence forassigning an uplink carrier switching configuration based on uplinkcarrier aggregation capabilities of a UE;

FIG. 13 is a flowchart of an embodiment method for assigning an uplinkcarrier switching configuration based on uplink carrier aggregationcapabilities of a UE;

FIG. 14 is a flowchart of an embodiment method for transmitting SRSsymbols;

FIG. 15 is a diagram of a network for supporting SRS switching;

FIG. 16 is a flowchart of an embodiment method for transmitting SRSsymbols;

FIG. 17 is a diagram of transmissions that occur prior to, andimmediately after, a UE 210 switches from a source component carrier toa target component carrier;

FIG. 18 is a diagram of transmissions that occur prior to, andimmediately after, a UE 210 switches from a source component carrier toa target component carrier;

FIG. 19 is a diagram of a frame format for an uplink control messagethat signals uplink and downlink RF re-tuning delays of a UE;

FIG. 20 is a flowchart of an embodiment method for signaling uplink anddownlink RF re-tuning delays of a UE;

FIG. 21 is a flowchart of an embodiment method 2100 for determininguplink and downlink RF re-tuning delays of a UE;

FIG. 22 is a diagram of an embodiment communications sequence foradapting a periodic SRS switching schedule in response to deactivationof a component carrier;

FIG. 23 is a flowchart of an embodiment method for adapting a periodicSRS switching schedule in response to deactivation of a componentcarrier;

FIGS. 24A-24D are diagrams of frame formats for control messages thatcarrying SRS instructions;

FIG. 25 is a flowchart of an embodiment method for locating an SRSinstruction in a control message;

FIG. 26 is a flowchart of another embodiment method for performingchannel estimation based on SRS symbols;

FIG. 27 is a diagram of uplink transmissions that occur prior to, andimmediately after, a UE switches from a source component carrier to atarget component carrier;

FIG. 28 is a flowchart of an embodiment method for puncturing an uplinksignal to compensate for an uplink RF re-tuning delay;

FIG. 29 is a diagram of transmissions that occur prior to, andimmediately after, a UE switches from a source component carrier to atarget component carrier;

FIG. 30 is a flowchart of an embodiment method for collision handlingduring SRS switching;

FIG. 31 is a diagram of a network for supporting SRS switching;

FIG. 32 is a diagram of a network for supporting SRS switching;

FIG. 33 is a diagram of transmissions that occur in a subframe during anSRS switching operation;

FIG. 34 is another diagram of transmissions that occur in a subframeduring an SRS switching operation;

FIG. 35 is yet another diagram of transmissions that occur in a subframeduring an SRS switching operation;

FIG. 36 is yet another diagram of transmissions that occur in a subframeduring an SRS switching operation;

FIG. 37 is yet another diagram of transmissions that occur in a subframeduring an SRS switching operation;

FIG. 38A is a diagram of an embodiment wireless network for supportingcarrier aggregation and/or carrier selection;

FIG. 38B is a diagram of an embodiment heterogeneous (Het-Net) forsupporting carrier aggregation and/or carrier selection;

FIG. 38C is a diagram of another embodiment Het-Net for supportingcarrier aggregation and/or carrier selection;

FIG. 39 is a flowchart of an embodiment method for performingsynchronization and measurement using reference signals;

FIG. 40 is a diagram of a carrier based SRS switching scheme;

FIG. 41 is a diagram of another carrier based SRS switching scheme;

FIG. 42 is a diagram of an embodiment multiple SRS switching operationsand SRS transmissions in one subframe;

FIG. 43 is a diagram of yet another carrier based SRS switching scheme;

FIG. 44A-44K illustrates embodiments of SRS switching operations withdifferent subframe types and RF architectures;

FIG. 45 is a diagram of yet another carrier based SRS switching scheme;

FIG. 46 is a diagram of yet another carrier based SRS switching scheme;

FIG. 47 is a diagram of yet another carrier based SRS switching scheme;

FIG. 48 is a diagram of yet another carrier based SRS switching scheme;

FIG. 49 is a diagram of yet another carrier based SRS switching scheme;

FIG. 50 is a diagram of yet another carrier based SRS switching scheme;

FIG. 51 is a diagram of yet another carrier based SRS switching scheme;

FIG. 52 is a diagram of yet another carrier based SRS switching scheme;

FIG. 53 is a diagram of yet another carrier based SRS switching scheme;

FIG. 54 is a diagram of yet another carrier based SRS switching scheme;

FIG. 55 illustrates a diagram of an embodiment processing system; and

FIG. 56 illustrates a diagram of an embodiment transceiver.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The structure, manufacture and use of the embodiments are discussed indetail below. It should be appreciated, however, that the presentdisclosure provides many applicable inventive concepts that can beembodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the invention, and do not limit the scope of the invention.

As mentioned above, carrier aggregation and carrier selection aretechniques that leverage multiple component carriers to increase theeffective bandwidth available to a given mobile device. As used herein,the term “component carrier” refers to a channel or carrier from atransmitter to a receiver. The terms “carrier,” “component carrier,”“aggregated carrier,” and “aggregated component carrier”, “servingcell”, “one of a PCell or SCell”, “one of a PCC or SCC” are usedinterchangeably throughout this disclosure.

During carrier selection/aggregation, a mobile device may be assigned aset of aggregated component carriers, and the base station may transmitdownlink signaling over one or more of those carriers at a given time.The mobile station may need to transmit sounding reference signal (SRS)symbols over each of the component carriers so that the base station cangenerate a channel estimate for the given component carrier, especiallyif channel reciprocity holds, such as for communications in an unpairedspectrum, e.g., a TDD carrier or an unlicensed spectrum or ahigh-frequency spectrum. The channel estimate may be used to selectwhich of the component carriers over which to perform downlinktransmissions, as well as to select the parameters used to transmit thedownlink signal(ing).

In some scenarios, a UE may be incapable of simultaneously transmittinguplink signaling over all component carriers in a set of aggregatedcomponent carriers assigned to the UE due to the number of transmit (TX)chains in the UE, or power limitations or PA limitations of the UE, orother limitations in the RF and/or baseband of the UE, or limitations inthe standards specifications, etc. In such scenarios, a UE may need toperform an SRS switching in order transmit SRS symbols over all of thecomponent carriers. In particular, a UE may transmit an SRS symbol overa current component carrier during an initial time period, switch fromthe current component carrier to a target component carrier, and thentransmit another SRS symbol over the current carrier during a subsequenttime period. As used herein, the term “current component carrier” refersto a component carrier that a UE is transitioning from during an SRSswitching operation, and the term “target component carrier” refers to acomponent carrier in which the UE is switching to during the SRSswitching operation.

Aspects of this disclosure provide embodiment signaling techniques,formats, and schemes for facilitating SRS switching during carrieraggregation/selection. It should be appreciated that the embodiment SRSswitching techniques herein may be applied in time division duplexed(TDD) channels, frequency division duplexed (FDD) channel, or channelsthat are both TDD and FDD. These embodiments may be employed in variouscommercial systems, such as wireless fiber to the X (WTTx) systems andthe like.

FIG. 1 illustrates a network 100 for communicating data. The network 100comprises UEs (or terminal, or device, etc.) 110 having a coverage area101, a base station 120, and a backhaul network 130. The base station120 may comprise any component capable of providing wireless access by,inter alia, establishing uplink (dashed line) and/or downlink (dottedline) connections with the UEs 110, such as a base station, an enhancedbase station (eNB), 5G gNB, a femtocell, small cell, pico cell,transmission point (TP), transmission-reception point (TRP), and otherwirelessly enabled devices. The UEs 110 may comprise any componentcapable of establishing a wireless connection with the base station 120.The backhaul network 130 may be any component or collection ofcomponents that allow data to be exchanged between the base station 120and a remote end (not shown). In some embodiments, the network 100 maycomprise various other wireless devices, such as relays, femtocells,etc.

In some situations, a UE that is assigned a set of aggregated componentcarriers for a carrier aggregation/switching transmissions scheme may beincapable of simultaneously transmitting uplink signals over allcomponent carriers in the assigned set of aggregated component carriers.FIG. 2 is a diagram of a network 200 for supporting carrieraggregation/switching transmissions. As shown, a UE is assigned a set ofaggregated component carriers 240 that includes component carriers241-249 associated with a base station 220. Each component carrier inthe set of aggregated component carriers 240 has a different carrierfrequencies (or center frequencies) (e.g., f₁, f₂, . . . f₉). Althoughthe labels (f₁, f₂, . . . f₅, f₆, f₇, . . . f₉) indicate that each ofthe component carriers 241-249 has a different sub-carrier frequencyband, it should be appreciated that those labels do not imply that theircorresponding sub-carrier frequencies are contiguous, or otherwiseconsecutive with one another, in the frequency domain. The differentcarriers may be in the same band, i.e., intra-band CA, or in differentbands, i.e., inter-band CA.

The UE 210 may receive downlink signals from, and/or transmit uplinksignals to, the base station 220 over one or more of the componentcarriers 241-249 in the set of aggregated component carriers 240according to a carrier aggregation and/or carrier selection transmissionscheme. In order to support carrier aggregation/selection, the basestation 220 may need to periodically, or aperiodically, perform channelestimation based on SRS symbols computed over the component carriers241-249, and the resulting channel estimate may be used by the basestation 220 to determine which of the component carriers 241-249 will beused for uplink/downlink data transmissions, as well as to selecttransmission parameters (such as beamforming or precoding parameters)for those uplink/downlink data transmissions. It should be appreciatedthat, channel estimation parameters that are generated by the basestation may be more accurate than channel estimation parametersgenerated, and fed-back, by the UE. Accordingly, the UE 210 may need totransmit SRS symbols 261-269 over the component carriers 241-249. Insome scenarios, the UE 210 may be incapable of simultaneouslytransmitting uplink signaling over all component carriers in the set ofaggregated component carriers 240, and as a result, may need to performSRS switching. In other scenarios, one or more carriers in the set ofaggregated component carriers in the set of aggregated componentcarriers 240 may be configured to support SRS symbol transmissionswithout supporting PUSCH/PUCCH transmissions, while other carriers inthe set of aggregated component carriers 240 are configured to supportboth SRS symbol transmissions and PUSCH/PUCCH transmissions. In suchscenarios, the UE 210 may need to perform SRS switching in order toperiodically, or aperiodically, transmit SRS symbols over the componentcarriers that do not support PUSCH/PUCCH transmissions. In this way, SRSswitching may occur even when the UE 210 is capable of simultaneouslytransmitting uplink signals over all component carriers in the set ofaggregated component carriers 240, in which case there may be no uplinkRF retuning delay associated with SRS switching. This scenario is alsoapplicable to the sets of aggregated component carriersdepicted/discussed in other sections of this application, e.g., thedescriptions of FIGS. 6, 15, etc.

Aspects of this disclosure provide embodiment signaling techniques,formats, and protocols for facilitating SRS switching during carrieraggregation/selection. In one embodiment, a radio resource control (RRC)message is used to signal a periodic SRS configurationparameter/instruction to a UE. FIG. 3 illustrates an embodimentcommunications sequence 300 for communicating an RRC message toconfigure a periodic SRS switching schedule. In this example, the basestation 220 transmits an RRC message 321 specifying a periodic SRSswitching parameter to the UE 210. The UE 210 then uses the periodic SRSswitching parameter to configure a periodic SRS switching schedule, andtransmits SRS symbols 361, 371, 381 over the component carrier 341during different intervals in a sequence of periodic intervals accordingto the periodic SRS switching schedule. Additionally, the UE 210transmits an SRS symbol 362 over the component carrier 342 and an SRSsymbol 375 over the component carrier 345. In this example, the SRSsymbol 362 is transmitted over the component carrier 342 in-between therespective transmissions of the SRS symbols 361 and 371 over thecomponent carrier 341, and the SRS symbol 375 is transmitted over thecomponent carrier 345 in-between the respective transmissions of the SRSsymbols 371 and 381 over the component carrier 341. Other examples arealso possible. The SRS symbol 362 may be one of a series of periodictransmissions over the component carrier 342. Alternatively, the SRSsymbol 362 may be an aperiodic transmission over the component carrierover the component carrier 342. Likewise, the SRS symbol 375 may eitherbe one of a series of periodic transmissions over the component carrier345 or an aperiodic transmission over the component carrier 345. In someinstances, a periodic SRS symbol may be referred to as a “trigger type 0SRS”, and an aperiodic SRS symbol may be referred to as a “trigger type1 SRS”. It should be appreciated that the fact that periodic SRS symbolsare generally be transmitted according to a periodic schedule, and thatthe fact that periodic SRS symbols may be referred to as “trigger type 0SRSs” does not imply that the periodic SRS symbols are somehow“triggered” by an aperiodically occurring event (e.g., a DCI message,etc.). In some embodiments, each component carrier that does not supportPUSCH signaling is associated with another component carrier that doessupport PUSCH signaling for SRS switching operation. In suchembodiments, no SRS transmissions may be permitted over the componentcarrier that does supports PUSCH signaling during a period in which SRStransmissions are performed over the component carrier that does notsupport PUSCH signaling, and vice versa. Techniques for triggeringaperiodic SRS symbol transmissions are discussed in greater detailbelow.

As mentioned above, the RRC message 321 carries, or otherwise indicates,a periodic SRS switching parameter. The periodic SRS switching parametermay be any parameter that can be used to generate, or otherwise, modifya periodic SRS switching schedule, such as a period between consecutiveintervals in the sequence of periodic intervals. The RRC message 321 mayalso specify other SRS parameters. In one example, the RRC message 321specifies orthogonal frequency division multiplexed (OFDM) orsingle-carrier frequency-division multiple access (SC-FDMA) symbollocations, in a subframe, over which the UE is transmit the SRS symbols.In other examples, the RRC message 321 specifies a number of SRS symbolsthat are to be transmitted during a given interval or series ofintervals and/or an SRS transmission parameter (e.g., a transmit powerlevel for the SRS symbols, etc.). FIG. 4 is a flowchart of an embodimentmethod 400 for transmitting SRS symbols according to a periodic SRSswitching schedule, as may be performed by a UE. At step 410, the UEreceives a radio resource control (RRC) message specifying a periodicSRS configuration parameter. At step 420, the UE configure a periodicSRS switching schedule based on the periodic SRS configuration parameterspecified by the RRC message. At step 430, the UE transmits SRS symbolsover a component carrier during periodic intervals in a sequence ofperiodic intervals according to periodic SRS switching schedule.

FIG. 5 is a flowchart of an embodiment method 500 for performing channelestimation according to a periodic SRS switching schedule, as may beperformed by a base station. At step 510, the base station transmits aradio resource control (RRC) message specifying a periodic SRSconfiguration parameter to a UE. At step 520, the base station receivesSRS symbols over a component carrier during a sequence of periodicintervals according to the periodic SRS configuration parameterspecified by the RRC message. At step 530, the base station performschannel estimation on the component carrier according to SRS symbolsreceived over the component carrier.

Downlink Control Information (DCI) messages may also be used to signalSRS configuration parameter/instruction to a UE. FIG. 6 illustrates anembodiment communications sequence 600 for communicating a DCI messageto specify or indicate a transmission parameter (e.g., power controlparameter) for a SRS transmission, or trigger an aperiodic SRS symboltransmission. As shown, the base station 220 transmits a DCI message 622to the UE 210. The DCI message 622 specifies an SRS configurationparameter. After receiving the DCI message 622, the UE 210 transmits anSRS symbol 672 over the component carrier 642 according to the SRSconfiguration parameter specified by the DCI message 622. The DCImessage 622 may have been transmitted over the component carrier 642.Alternatively, the DCI message 622 may have been transmitted over adifferent component carrier.

In one example, the DCI message 622 triggers transmission of the SRSsymbol 672 over the component carrier 642. In such an example, the DCImessage 622 may have been communicated over the component carrier 642.Alternately, the DCI message 622 may have been communicated over one ofthe component carrier 641, 645 (e.g., over a primary cell or primarycomponent carrier (PCC) configured for PUCCH and/or PUSCHtransmissions), in which case the DCI message 622 would trigger across-carrier transmission of the SRS symbol 672 over the componentcarrier 642.

The DCI message 622 may have instructed the UE 210 to transmit the SRSsymbol 672 in-between transmissions of the SRS symbol 671 and the SRSsymbol 681 over the component carrier 641. For instance, the UE 210 mayhave been transmitting the SRS symbols 661, 671, 681 over the componentcarrier 641 according to a periodic SRS switching schedule, and the DCImessage 622 may instruct the UE 210 to perform an aperiodic SRStransmission over the component carrier 642 in-between the periodictransmissions over the component carrier 641. In this way, the DCImessage 622 may prompt the UE 210 to switch from the component carrier641 to the component carrier 642 after transmission of the SRS symbol671, transmit the SRS symbol 672 over the component carrier 642, andthen switch back to the component carrier 641 so that the SRS symbol 681can be transmitted during the next available periodic interval. This mayor may not entail delaying transmission of the SRS symbol 681 for aperiodic interval, depending on whether an uplink radio frequency (RF)retuning delay of the UE 210 permits the UE 210 to perform the SRSswitching operations in-between consecutive periodic intervals. The DCImessage 622 may indicate other types of SRS configuration parameters,instead of (or in addition to) triggering an aperiodic SRS transmission.For example, the DCI message 622 may specify a transmission parameter ofthe SRS symbol 672, e.g., an SRS transmit power level, etc.

FIG. 7 is a flowchart of an embodiment method 700 for performingaperiodic SRS transmissions, as may be performed by a UE. At step 710,the UE monitors a physical downlink control channel (PDCCH) for aDownlink Control Information (DCI) message. At step 720, the UE detectsa DCI message specifying an SRS configuration parameter. At step 730,the UE transmits an SRS symbol over a component carrier according to theSRS configuration parameter specified by the DCI message.

FIG. 8 is a flowchart of an embodiment method 800 for performing channelestimation according to an aperiodic SRS transmission, as may beperformed by a base station. At step 810, the base station transmits aDownlink Control Information (DCI) message specifying an SRSconfiguration parameter to a UE. At step 820, the base station receivesan SRS symbol over a component carrier according to an SRS configurationparameter. At step 830, the base station generates a channel estimatefor a component carrier according to the SRS symbol.

DCI message are typically decoded by the UE through a process referredto as blind detection. Blind detection reduces network overhead byallowing UEs to detect which set of control channel elements (CCEs) in aphysical downlink control channel (PDCCH) carry a DCI message for the UEwithout having to send explicit control signaling. In general, a UEperforms blind detection in a search space of a physical downlinkcontrol channel (PDCCH) by attempting to decode different sets ofcontrol channel elements (CCEs) according to known DCI formats. SinceSRS switching is a new technique, many UEs may not know what DCI formatsare associated with specific SRS configuration parameters/instructions.Embodiments of this disclosure use RRC messages to notify UEs of a DCImessage format associated with an SRS parameter. This allows the UE tomonitor a physical downlink control channel (PDCCH) for the DCI format,and vary their SRS transmission/switching operations accordingly.

FIG. 9 illustrates an embodiment communications sequence 900 for usingan RRC message to notify a UE of a DCI format that will be used tosignal an SRS configuration parameter over a PDCCH. As shown, the basestation 220 transmits an RRC message 921 to the UE 210. The RRC message921 configures that a DCI message format is associated with a specificSRS signaling instruction. For example, the RRC message 921 may specifya specific DCI message format for indicating an SRS transmit powerlevel. As another example, the RRC message 921 may specify a specificDCI message format for triggering an SRS symbol transmission over thesame component carrier used to transmit the DCI message. As yet anotherexample, the RRC message 921 may specify a specific DCI message formatfor triggering cross-carrier transmission of an SRS symbol over adifferent component carrier than the one used to transmit the DCImessage. As yet another example, the RRC message 921 may specify aspecific DCI message format for triggering an SRS symbol transmissionand the associated SRS transmission power level, for the same ordifferent CC, for one or multiple CCs, for one or multiple UEs.Thereafter, the base station 220 transmits a DCI message 922 having theDCI format indicated by the RRC message 921 to the UE 210. The UE 210detects the DCI message 922 by monitoring a PDCCH for the DCI messageformat indicated by the RRC message 921, and transmits an SRS symbol 972over the component carrier 942 according to the SRS configurationparameter associated with the DCI message 922. The DCI message 922 mayhave been transmitted over the component carrier 942 or over a differentcomponent carrier.

FIG. 10 is a flowchart of an embodiment method 1000 for performingaperiodic SRS transmissions based on DCI message formats communicatedover a PDCCH, as may be performed by a UE. At step 1010, the UE receivesa radio resource control (RRC) message specifying a downlink controlinformation (DCI) message format for signaling an SRS parameter. At step1020, the UE monitors a physical downlink control channel (PDCCH) forthe DCI message format specified by the RRC message. At step 1030, theUE detects a DCI message having the DCI message format in the PDCCH. Atstep 1040, the UE transmits an SRS symbol over a component carrieraccording to the SRS configuration parameter associated with the DCImessage format.

FIG. 11 is a flowchart of an embodiment method 1100 for performingchannel estimation according to SRS transmissions, as may be performedby a base station. At step 1110, the base station transmits a RadioResource Control (RRC) message specifying a Downlink Control Information(DCI) message format for signaling an SRS parameter. At step 1120, thebase station transmits a DCI message having the DCI format over aphysical downlink control channel (PDCCH). At step 1130, the basestation receives an SRS symbol over a component carrier according to theSRS configuration parameter. At step 1140, the base station generates achannel estimate for the component carrier according to the SRS symbol.

Different UEs may have different uplink carrier aggregationcapabilities. For example, some UEs may be able to simultaneouslytransmit uplink signals and/or receive downlink signals over differentnumbers of component carriers. Additionally, UEs may have differentuplink RF retuning delays. The RF retuning delays may also be referredto as RF retuning times, RF retuning gaps, or in the context of SRSswitching, SRS switching gaps, SRS switching times, etc. Embodiments ofthis disclosure allow base stations to tailor an uplink carrierswitching configuration for a given UE based on uplink carrieraggregation capabilities of the UE.

FIG. 12 illustrates an embodiment communications sequence 1200 forassigning an uplink carrier switching configuration for a given UE basedon uplink carrier aggregation capabilities of the UE. As shown, the UE210 reports uplink carrier aggregation capabilities 1221 to the basestation 220. The uplink carrier aggregation capabilities 1221 mayspecify the number of component carriers that the UE 210 is capable oftransmitting uplink signals over at the same time and/or an uplink RFretuning delay of the UE 210. The base station 220 may then assign anuplink carrier switching configuration 1222 to the UE based on theuplink carrier aggregation capabilities 1221, and send the uplinkcarrier switching configuration 1222. The uplink carrier switchingconfiguration 1222 may be communicated in various ways, such as viahigher-layer signaling channel (e.g., in an RRC message), media accesscontrol (MAC) signaling channel, or a PDCCH (e.g., in a DCI message).Upon reception, the UE may transmit SRS symbols 1261, 1262, 1263 overthe component carriers 1241, 1242, 1245 according to the uplink carrierswitching configuration 1222.

FIG. 13 is a flowchart of an embodiment method 1300 for assigning anuplink carrier switching configuration to a UE based on uplink carrieraggregation capabilities of the UE, as may be performed by a basestation. At step 1310, the base station receives an uplink controlsignal indicating uplink carrier aggregation capabilities of a UE. Atstep 1320, the base station assigns an uplink carrier switchingconfiguration to the UE based on the carrier aggregation capabilities ofthe UE. At step 1330, the base station sends a downlink control signalinstructing the UE to transmit an SRS symbol over a set of aggregatedcomponent carriers based on the uplink carrier switching configuration.

FIG. 14 is a flowchart of an embodiment method 1400 for performing SRStransmissions over component carriers, as may be performed by a UE. Atstep 1410, the UE transmits an uplink control signal indicating uplinkcarrier aggregation capabilities of UE. At step 1420, the UE receives anuplink carrier switching configuration from the base station. At step1430, the UE transmits an SRS symbol over a component carrier accordingto uplink carrier switching configuration.

In some embodiments, a UE may be assigned different sets of aggregatedcomponent carriers associated with different base stations. FIG. 15 is adiagram of a network 1500 in which the UE 210 is assigned a set ofaggregated component carriers 1540 associated with the base station 220,as well as a set of aggregated component carriers 1550 associated with abase station 230. Each component carrier in the set of aggregatedcomponent carriers 1540, as well as the set of aggregated componentcarriers 1550, has a different sub-carrier frequency, as indicated bythe labels (f1, f2, . . . f5, f6, f7 . . . f9). It should be appreciatedthat subscripts in the labels (f1, f2, . . . f5, f6, f7 . . . f9) do notimply, or otherwise denote, a relationship/order between sub-carrierfrequencies of the corresponding component carriers 1541-1545,1556-1557. By way of example, component carrier 1541 may have a highersub-carrier frequency than component carrier 1542 in some embodiments,and a lower sub-carrier frequency than component carrier 1542 in otherembodiments. Likewise, component carriers in a given set of aggregatedcomponent carriers are not necessarily contiguous, or otherwiseconsecutive with one another, in the frequency domain. By way ofexample, one or more sub-carrier frequencies of individual componentcarriers 1541, 1542, 1545 in the set of aggregated component carriers1540 may be interleaved with one or more sub-carrier frequencies ofindividual component carriers 1551, 1552, 1555 in the set of aggregatedcomponent carriers 1550.

The UE 210 may receive downlink signals from, and/or transmit uplinksignals to, the base station 220 over one or more of the componentcarriers 1541-1545 in the set of aggregated component carriers 1540according to a carrier aggregation and/or carrier selection transmissionscheme. Likewise, the UE 210 may receive downlink signals from, and/ortransmit uplink signals to, the base station 230 over one or more of thecomponent carriers 1551-1555 in the set of aggregated component carriers1550 according to a carrier aggregation and/or carrier selectiontransmission scheme. The BS 220, 230 may be connected via a fastbackhaul, which may be used to communicate data and/or control signalingrelated to carrier aggregation and/or coordinated multipoint (CoMP)transmissions. Alternatively, the BS 220 and 230 may be connected withnon-ideal backhaul, and the scenario may be corresponding to a dualconnectivity scenario and have multiple TAGs. Both are considered inthis disclosure.

The base stations 220, 230 may be required to periodically, oraperiodically, perform channel estimation over the component carriers1541-1545 and the component carriers 1551-1555 (respectively) in orderto select which component carrier(s) will be used for uplink/downlinkdata transmissions, as well as to select the transmission parameters forthe uplink/downlink data transmissions. Accordingly, the UE 210 may needtransmit SRS symbols 1521, 1522, 1525 over the component carriers 1541,1542, 1545 (respectively), as well as transmit SRS symbols 1566, 1567,1569 over the component carriers 1556, 1557, 1559 (respectively). Insome embodiments, the UE 210 may be incapable of simultaneouslytransmitting uplink signaling over all component carriers in the set ofaggregated component carriers 1540 and/or the set of aggregatedcomponent carriers 1550, and as a result, may be required to perform SRSswitching.

Notably, the propagation delay between the UE 210 and the base station220 may be different than the propagation delay between the UE 210 andthe base station 230. Because of this, uplink transmissions over thecomponent carriers 1541, 1542, 1545 may require a different timingadvance (TA) adjustment than uplink transmissions over componentcarriers 1541, 1542, 1545. In general, an initial uplink TA adjustmentvalue is determined by random access procedure. In particular, the UE210 generally would transmit random access preambles to the basestations 220, 230, which would then estimate a respective TA value basedon a propagation delay associated with the random access preamble, senda corresponding random access response (RAR) specifying the TA value tothe UE 210. Thereafter, the UE 210 would use the initial TA value totransmit SRS symbols, and other data, over the PUCCHs and/or PUSCHs, andthe base stations 220, 230 would continuously update the TA values basedon propagation delays measured according to the SRS symbols.

Having to perform a random access procedure may introduce significantlatency into SRS switching procedures, as exchanging the random accesspreamble and/or RAR messages prior to SRS symbol transmission may undulydelay the SRS symbol transmission. To mitigate the latencies associatedwith random access procedures during SRS switching, the base station 220sends a dual connectivity constraint 1522 to the UE 210. The dualconnectivity constraint 1522 prohibits the UE 210 from switching from asource component carrier in the set of aggregated component carriers1540 to a target component carrier in the set of aggregated componentcarriers 1550 during a set of time periods, and vice versa. Although thedual connectivity constraint 1522 is depicted as being transmitted bythe base station 220, it should be appreciated that dual connectivityconstraints can be transmitted by any network-side device, such as thebase station 230 or a separate network controller.

In one example, the UE 210 accomplishes this by using different transmitchains (TX chains) to transmit uplink signaling over the respective setsof aggregated component carriers 1540, 1550. By way of example, the UE210 may use the first TX chain 219 to transmit the SRS symbols 1561,1562, 1565 over the component carriers 1541, 1542, 1545 (respectively)without using the TX chain 218 to transmit any of the SRS symbols 1566,1567, 1569 over the component carriers 1556, 1557, 1559. Likewise, theUE 210 may use the TX chain 219 to transmit the SRS symbols 1565, 1566,1569 over the component carriers 1555, 1556, 1559 (respectively) withoutusing the TX chain 219 to transmit any SRS symbol over componentcarriers 1541, 1542, 1545 in the set of aggregated component carriers1540.

FIG. 16 is a flowchart of an embodiment method 1600 for transmitting SRSsymbols over different sets of aggregated component carriers based on adual connectivity constraint, as may be performed by a UE. At step 1610,the UE receives a downlink control signal specifying a dual connectivitycell group configuration constraint from a network controller. At step1620, the UE uses a first transmission chain (TX chain) to transmit SRSsymbols over component carriers in monitored by a first base stationwithout switching the first TX chain to a target component carriermonitored by a second base station. At step 1630, the UE uses a secondTX chain to transmit SRS symbols over component carriers monitored bythe second base station without switching the second TX chain to atarget component carrier monitored by the first base station.

The dual connectivity constraint may be primarily used when there is nofast backhaul between base stations 220 and 230, and may not be appliedin scenarios where there is a fast backhaul connection between the basestations 220 and 230.

When a TX and/or RX chain is adjusted switched from a source componentcarrier to a target component carrier, there is generally an RF retuningdelay associating with adjusting hardware components of the TX or RXchain from source sub-carrier frequency to the target sub-carrierfrequency.

The downlink RF retuning delay of a UE may be approximately equal to anuplink RF retuning delay of the UE in instances where both a TX chainand an RX chain are switched from a source component carrier to a targetcomponent carrier. FIG. 17 illustrates an example of transmissions thatoccur prior to, and immediately after, the UE 210 is switched from asource component carrier to a target component carrier at period t₃. Inthis example, an RX chain 214 of the UE 210 is used to receive both thedownlink signal 1714 over the source component carrier and the downlinksignal 1724 over the target component carrier, and the TX chain 218 ofthe UE 210 is used to transmit both the uplink signal 1712 over thesource component carrier and the uplink signal 1722 over the targetcomponent carrier. Because of this, both the TX chain 218 and the RXchain 214 need to be adjusted to the center frequency of the targetcomponent carrier when the UE 210 switches to the target componentcarrier at the beginning of period t₄, and as a result, both thedownlink RF re-tuning delay and the uplink RF retuning delay have aduration that is approximately equal to period t₄. Consequently, thebase station associated with the target component carrier should notbegin sending the downlink transmission 1724 until period t₅ and shouldnot expect to begin receiving the uplink transmission 1722 until periodt₅. Other examples may also exist, such as when component carriers aretime division duplexed (TDD) such that uplink and downlink transmissionsdo not overlap in the time domain. In such examples, SRS switching maybe performed for an uplink TX chain, and the downlink RX chain maymonitor both the source and target component carriers at the same timewithout switching.

The downlink RF retuning delay of a UE may be approximately zero, orotherwise much less than the uplink RF retuning delay of the UE, ininstances where only the TX chain of the UE is switched from a sourcecomponent carrier to a target component carrier, as may occur ininstances where the UE includes sufficiently decoupled RX chainsassigned to the source and target component carriers.

FIG. 18 illustrates an example of transmissions that occur prior to, andimmediately after, a UE 210 is switched from a source component carrierto a target component carrier. In this example, an RX chain 216 of theUE 210 is used to receive the downlink signal 1814 over the sourcecomponent carrier, an RX chain 217 of the UE 210 is used to receive thedownlink signal 1824 over the target component carrier, and the TX chain218 of the UE 210 is used to transmit both the uplink signal 1812 overthe source component carrier and the uplink signal 1822 over the targetcomponent carrier, via carrier switching. Because of this, only the TXchain 218 needs to be adjusted to the center frequency of the targetcomponent carrier when the UE 210 switches to the target componentcarrier at the beginning of period t4. As a consequence, the UE 210experiences minimal downlink RF re-tuning delay, meaning that the basestation associated with the target component carrier may begin thedownlink transmission 1824 during period t₄, but should not expect tobeing receiving the uplink transmission 1822 until period t₅. Otherexamples may also exist, such as when component carriers are timedivision duplexed (TDD) such that uplink and downlink transmissions donot overlap in the time domain. In such examples, SRS switching may beperformed for an uplink TX chain, and the downlink RX chain may monitorboth the source and target component carriers at the same time withoutswitching.

Because the duration of a UE's uplink/downlink RF retuning delays impactthe timing of uplink and downlink transmissions over the targetcomponent carrier, it may be helpful, or even necessary, for a UE tonotify a base station of those RF retuning delays. Embodiments of thisdisclosure provide a low-overhead frame format for signaling a UE'suplink/downlink RF retuning delays. FIG. 19 is a diagram of a frameformat of an uplink control message 1901 for signaling uplink anddownlink RF re-tuning delays of a UE. The uplink control message 1901includes an uplink RF retuning delay field 910 and a flag field 920. Theuplink RF retuning delay field 910 may consists of two or more bitsindicating a duration of a UE's uplink RF retuning delay. The bits mayexpress the duration of the UE's uplink RF retuning delay as fractionsof an OFDM symbol duration, e.g., 0 symbol duration, 0.5 symbolduration, 1 symbol duration, 1.5 symbol duration, etc. The flag field920 may consist of a single bit that either is set to a first value toindicate that a downlink RF retuning delay of the UE is equal to theuplink RF retuning delay indicated by the field 910 or is set to asecond value to indicate that the downlink RF retuning delay of the UEis equal to zero (or is otherwise below a lower threshold).

FIG. 20 is a flowchart of an embodiment method 2000 for signaling uplinkand downlink RF re-tuning delays of a UE, as may be performed by the UE.At step 2010, the UE sets an uplink RF retuning delay field of an uplinkcontrol message to indicate a duration of the UE's uplink RF retuningdelay. At step 2020, the UE sets a flag field of the uplink controlmessage according to a downlink RF retuning delay. In particular, the UEsets the flag field to a first value when the downlink RF retuning delayof the UE is equal to the uplink RF retuning delay or to a second valuewhen the downlink RF retuning delay of the UE is equal to zero (or isotherwise below a lower threshold). The flag field may be referred to asa downlink RF retuning field in some cases.

FIG. 21 is a flowchart of an embodiment method 2100 for determininguplink and downlink RF re-tuning delays of a UE, as may be performed bya base station. At step 2110, the base station Receives an uplinkcontrol message from the UE. At step 2120, the base station determinesan uplink RF retuning delay of the UE according to an uplink RF retuningdelay field of the uplink control message. At step 2130, the basestation determines a downlink RF retuning delay of the UE according to aflag field of the uplink control message.

As discussed above, a UE may be instructed to periodically transmit SRSsymbols over component carriers in a set of aggregated componentcarriers according to a periodic SRS switching schedule. In some cases,one of the component carriers in the set of aggregated componentcarriers may be deactivated before a duration of the periodic SRSswitching schedule is over. In such a case, the UE may need to adapt theperiodic SRS switching schedule to compensate for the deactivatedcarrier. In embodiments of this disclosure, a UE is preconfigured toadapt the periodic SRS switching schedule in the event that a componentcarrier is deactivated.

FIG. 22 illustrates an embodiment communications sequence 2200 foradapting a periodic SRS switching schedule in response to deactivationof a component carrier. In this example, the UE 210 has been instructedto periodically transmit SRS symbols over component carriers 2241, 2242,2243 in a set of aggregated component carriers 1240. Accordingly, the UE210 periodically transmits the SRS symbols 2261-2268 over the componentcarriers 2241, 2242, 2243 during a first set of time periods. At somepoint before the duration of the SRS switching schedule ends, the UE 210receives a deactivate component carrier message 1222 indicating that thecomponent carrier 2242 has been deactivated. The UE 210 is preconfiguredto adapt the SRS switching schedule to compensate for deactivation ofthe component carrier 2242, and as a result the UE 210 transmits the SRSsymbols 2271-2283 over the component carriers 2241, 2243 during a secondset of time periods without transmitting any SRS symbols over thedeactivated component carrier 2242 during the second set of timeperiods.

FIG. 23 is a flowchart of an embodiment method 2300 for adjusting aperiodic SRS transmission schedule in response to activation of acomponent carrier, as may be performed by a UE. At step 2310, the UEtransmits at least one SRS symbol over each component carrier in a setof aggregated component carriers according to SRS switchingconfiguration during a first set of time periods. At step 2320, the UEreceives a control message indicating deactivation of at least onecomponent carrier in the set of aggregated component carriers. Thecontrol message may be a media access control (MAC) message, or anothertype of control message (E.g., a DCI message, an RRC message, etc.), orimplicit via an expiration of an activation timer not reset due to newactivities. At step 2330, the UE adjusts the periodic SRS switchingschedule to compensate for the deactivated component carrier. Thisadjustment may include re-assigning periodic SRS symbol transmissionsfrom the deactivated component carrier to one of the remaining activecomponent carriers. Alternatively, the adjustment may include removingthe deactivated component carrier from the periodic schedule (e.g., around robin schedule, etc.), such that SRS symbols are transmitted overthe remaining activate component carriers on a more frequent basis. Atstep 2340, the UE transmits at least one SRS symbol over each remainingcomponent carrier in the set of aggregated component carriers accordingto the adjusted periodic SRS switching schedule during a second set oftime periods without transmitting any SRS symbols over the at least onedeactivated component carrier during the second set of time periods.

In some scenarios, a base station may want to broadcast a controlmessage that includes multiple SRS parameters (including SRS powercontrol and/or SRS triggers) for one or multiple UEs. Embodiments ofthis disclosure communicate flag bits within the control message, orseparately via higher-layer signaling, that notify the individual UEs ofthe location of their corresponding SRS instruction amongst the multipleSRS instructions embedded within the control message. FIGS. 24A-24Dillustrate frame formats for control messages 2410, 2420, 2430, 2440carrying multiple SRS instructions 2456-2459. Each of the SRSinstructions 2456-2459 may be intended for a different UE, and may havedifferent lengths depending on the information (e.g., SRS parameters,etc.) being conveyed by the SRS instructions.

As shown in FIG. 24A, the control message 2410 includes flag bits2411-2419 and the SRS instructions 2456-2459. The flag bits 2411-2419can be used to locate the SRS instructions 2456-2459 within the controlmessage 2410. The flag bit 2411 indicates a starting bit location (B1)for the SRS instruction 2456. The flag bit 2416 indicates a length (L1)of the SRS instruction 2456. The flag bits 2411, 2416 can therefore beused by a corresponding UE to identify the location of the SRSinstruction 2456. Likewise, the flag bit 2412 indicates a starting bitlocation (B₂) for the SRS instruction 2457, the flag bit 2417 indicatesa length (L₂) of the SRS instruction 2457, the flag bit 2414 indicates astarting bit location (B_(N)) for the SRS instruction 2459, and the flagbit 2419 indicates a length (L_(N)) of the SRS instruction 2456.

Similarly, as shown in FIG. 24B, the control message 2420 includes flagbits 2421-2424 that can be used to locate the SRS instructions 2456-2459within the control message 2410. The flag bit 2421 indicates a length(L1) of the SRS instruction 2456, the flag bit 2422 indicates a length(L₂) of the SRS instruction 2457, and the flag bit 2424 indicates alength (L_(N)) of the SRS instruction 2459. The starting bit location(B1) of the SRS instruction 2456 may be a priori information of UEs thatreceive the control message 2420. Alternatively, the starting bitlocation (B1) of the SRS instruction 2456 may be signaled by a separateflag bit that is not shown in FIG. 24B. Based on knowledge of thestarting bit location (B1) of the SRS instruction 2456, an intendedrecipient of the SRS instruction 2456 can use the flag bit 2421 tolocate the SRS instruction 2456. Likewise, an intended recipient of theSRS instruction 2457 determine the starting bit location (B2) of the SRSinstruction 2457 by adding the number of bits indicated by the flag bit2421 to the starting bit location (B1) of the SRS instruction 2456, andthen use the flag bit 2422 to locate the SRS instruction 2457. In asimilar way, an intended recipient of the SRS instruction 2459 can add asummation of the number bits indicated by all flag bits preceding theflag bit 2424 to the starting bit location (B1) to determine thestarting bit location (BN) of the SRS instruction 2459, and then use theflag bit 2424 to locate the SRS instruction 2457.

In the control message 2430 depicted by FIG. 24C, the flag bits2431-2434 are interleaved with their corresponding SRS instructions2456-2459. Similar to the control message 2420, the flag bit 2431indicates a length (L1) of the SRS instruction 2456, the flag bit 2432indicates a length (L₂) of the SRS instruction 2457, and the flag bit2434 indicates a length (L_(N)) of the SRS instruction 2459. An intendedrecipient of the SRS instruction 2456 can use the flag bit 2431 tolocate the SRS instruction 2456. An intended recipient of the SRSinstruction 2457 can use the flag bit 2431 to locate the flag bit 2432,and the use the flag bit 2432 to locate the SRS instruction 2457. Theintended recipient of the SRS instruction 2459 can locate the flag bit2439 based on all of the flag bits preceding the flag bit 2439, and thenuse the flag bit 2439 to locate the SRS instruction 2459. As yet anotheralternative, one or more of the flag bits discussed above may betransmitted via higher layer signaling, and then used to locate the SRSinstructions 2456-2459 in the control message 2440 depicted by FIG. 24D.

FIG. 25 is a flowchart of an embodiment method 2500 for locating an SRSparameter in a control message, as may be performed by a UE. At step2510, the UE receives a single downlink control message includingmultiple SRS parameters and one flag field. At step 2520, the UEIdentifies the location of an SRS instruction, amongst the multiple SRSinstructions in the single downlink control message, based on the flagfield. At step 2530, the UE transmits an SRS symbol over a componentcarrier based on the SRS instruction.

FIG. 26 is a flowchart of an embodiment method 2600 for sending acontrol message that includes SRS instructions for different UEs, as maybe performed by a base station. At step 2610, the base station generatesa single downlink control message including multiple SRS instructions.At step 2620, the base station generates one flag field for each SRSinstruction based on the location and/or length of the SRS instruction.At step 2630, the base station transmits the single downlink controlmessage and the flag fields to the UEs. At step 2640, the base stationreceives SRS symbols from UEs according to the SRS instructions embeddedin the single downlink control message. At step 2650, the base stationgenerates channel estimates according to the SRS symbols.

In some embodiments, a UE may puncture a portion of an uplink signaltransmitted over a target component carrier that overlaps with an uplinkRF retuning delay after switching from a source component carrier to thetarget component carrier. FIG. 27 illustrates uplink transmissions 2730that occur prior to, and immediately after, a UE 210 switches from asource component carrier to a target component carrier. In this example,a TX chain 218 of the UE 210 is used to transmit both the uplink signal2720 over the source component carrier and the uplink signal 2730 overthe target component carrier. As a consequence, the UE 210 an uplink RFretuning delay with a duration equal to period t₄. In this example, theuplink transmission 2730 is scheduled over periods t₄ through t₁₀. Tocompensate for the uplink RF retuning delay, the UE 210 punctures aportion 2731 of the uplink transmission 2730 that overlaps with theperiod t₄. In one embodiment, the UE 210 may perform a rate adjustment(e.g., rate matching) for the non-punctured portion of the uplinktransmission 2730 to compensate for bandwidth lost from puncturing theportion 2731. The puncturing may occur on the source component carrierand/or on the target component carrier. Similarly, puncturing or ratematching in DL may also occur.

FIG. 28 is a flowchart of an embodiment method 2800 for compensating foran uplink RF retuning delay after switching from a source componentcarrier to a target component carrier, as may be performed by a UE. Atstep 2810, the UE transmits a first uplink signal carrying at least afirst SRS symbol over a first component carrier. At step 2820, the UEswitches from the source component carrier to a target component carrieraccording to an SRS switching schedule. At step 2830, the UE punctures aportion of a second uplink signal corresponding to a duration of anuplink RF retuning delay. At step 2840, the UE transmits the seconduplink signal over the target component carrier.

Embodiments of this disclosure provide techniques for handlingscheduling conflicts between SRS symbols and other uplink signals. Inparticular, some types of uplink signals may be scheduled over a primarycomponent carrier at the same time in which the UE is scheduled totransmit an SRS symbol over a secondary component carrier. If the uplinksignal scheduled over the primary component carrier satisfies acriterion, then the UE may prioritize transmission of the uplink signalover the primary component carrier, and delay, or otherwise cancel, thescheduled transmission of the SRS symbol over the secondary componentcarrier.

FIG. 29 illustrates transmissions that occur prior to, and immediatelyafter, a UE 210 switching from a primary component carrier to asecondary component carrier. In this example, a TX chain 214 of the UE210 is used to transmit both receive the downlink signal 2912 andtransmit the uplink acknowledgement (ACK) and/or NACK message 2914 overthe primary component carrier, as well as to transmit the SRS symbol2924 over the secondary component carrier. The ACK message 2914indicates to a base station associated with the primary componentcarrier that the downlink transmission 2912 was successfully decoded bythe UE. The ACK message 2914 is scheduled to be transmitted over theprimary component carrier during the same period t₇ in which the SRSsymbol 2924 is initially scheduled to be transmitted over the secondarycomponent carrier. In this example, the ACK message 2914 is givenprecedent, and the SRS symbol is delayed until period t₉. The period t9may be the next-available opportunity for transmitting the SRS symbol2924 over the secondary component carrier. In other examples, the SRSsymbol may be delayed indefinitely.

Although in FIG. 29, the ACK message 2914 is prioritized over the SRSsymbol 2924, it should be appreciated that other uplink symbols (e.g.,channel state information (CSI) messages, etc.) may also be givenpriority over an SRS symbol transmission.

FIG. 30 is a flowchart of an embodiment method 2800 for collisionhandling during SRS switching, as may be performed by a UE. At step3010, the UE determines that an uplink signal is scheduled over aprimary component carrier during the same time period as an SRS symbolis scheduled to be transmitted over a primary component carrier. At step3020, the UE transmits the uplink control signal over the primarycomponent carrier during the time period without transmitting SRS symbolover the secondary component carrier during the time period.

In some embodiments, groups of component carriers being monitored by thesame may be associated with a common timing advance group (TAG). One ormore component carriers in a timing advance group may not supportPUCCH/PUSCH signaling. FIG. 31 is a diagram of a network 3000 in whichthe UE 210 is assigned component carriers 3141, 3142, 3145 associatedwith a first TAG (TAG #1), as well as component carriers 3156, 3157,3159 assigned to a second TAG (TAG #2). The UE 210 may use the same TAadjustment value when transmitting uplink signals (e.g., SRS symbols,etc.) over the component carriers 3141, 3142, 3145 associated with theTAG #1. Likewise, the UE 210 may use the same TA adjustment value whentransmitting uplink signals (e.g., SRS symbols, etc.) over the componentcarriers 3156, 3157, 3159 assigned to the TAG #2. In this example, thecomponent carrier 3142 and the component carrier 3157 do not supportPUCCH/PUSCH signaling.

FIG. 32 is a diagram of a network 3200 in which a UE 210 transmits SRSsymbols over component carriers 3241-3243 in the group of aggregatedcomponent carriers 3240, as well as over component carriers 3254-3256 inthe group of aggregated component carriers 3250. Component carriers3241-3243 in the group of aggregated component carriers 3240 supportPUCCH/PUSCH signaling, while component carriers 3254-3256 in the groupof aggregated component carriers 3250 do not support PUCCH/PUSCHsignal(ing), and only SRS and possibly RACH may be supported. The UE 210receives downlink signaling from the network over component carriers3241-3243 in the group of aggregated component carriers 3240 andcomponent carriers 3254-3256 in the group of aggregated componentcarriers 3250, as well as over component carriers 3267-3269. Thedownlink signaling may be received over two or more of the componentcarriers 3241-3243, 3254-3256, 3267-3269 in instance where carrieraggregation is applied.

In some embodiments, an uplink RF tuning delay may be experienced duringSRS switching. FIG. 33 is a diagram of uplink transmissions that occurduring an SRS switching operation. In this example, a TX chain 218 ofthe UE 210 is used to transmit the uplink signal 3220 over the sourcecomponent carrier and the SRS symbol 3332 over the target componentcarrier. The UE 210 experiences an uplink RF retuning delay with aduration equal to period t₉. The uplink signal 3320 carries an SRSsymbol 3322. Transmission characteristics of the SRS symbol 3322, suchas a transmit power level, may be based on characteristics of aPUSCH/PUCCH signaling in the uplink signal 3320. Transmissioncharacteristics of the SRS symbol 3332 may be independent of PUSCH/PUCCHsignaling.

In some embodiments, SRS switching is performed over a time divisionduplexed (TDD) channel. FIG. 34 is a diagram of transmissions that occurin a subframe 3400 during an SRS switching operation. switches from asource component carrier to a target component carrier. In this example,a transceiver (TX/RX) chain 212 of the UE 210 is used to both receive adownlink transmission 3412 over the source component carrier, and totransmit an SRS symbol 3424 and an uplink signal 3422 over the targetcomponent carrier. The UE 210 has an RF retuning delay with a durationthat is less than the guard interval between an uplink portion 3420 ofthe subframe 3400 and a downlink portion 3410 of the subframe 3400. As aresult, switching the TX/RX chain 212 from the source component carrierto the target component carrier does not interfere with the downlinktransmission 3412.

FIG. 35 is a diagram of transmissions that occur in a subframe 3500during an SRS switching operation. In this example, the TX/RX chain 212of the UE 210 is used to both receive a downlink transmission 3512 overthe source component carrier, and transmit an SRS symbol 3524 and anuplink signal 3522 over the target component carrier. Because an RFretuning delay of the TX/RX chain 212 has a duration that exceeds theguard interval between an uplink portion 3520 of the subframe 3500 and adownlink portion 3510 of the subframe 3500, switching the TX/RX chain212 from the source component carrier to a target component carrierinterferes with, or otherwise requires a shortening or puncturing ordropping on one or more symbols of, the downlink transmission 3512.

FIG. 36 is a diagram of transmissions that occur in a subframe 3600during an SRS switching operation. In this example, an RX chain 216 ofthe UE 210 is used to receive a downlink transmission 3612 over thesource component carrier, and a TX chain 218 is used to transmit both anSRS symbol 3622 over the target component carrier and the uplink signal3614 over the source component carrier. Hence, the TX chain 218 isswitched from the source component carrier to the target componentcarrier prior to transmission of the SRS symbol 3622, and then back tothe source component carrier prior to transmission of the uplink signal3614. Although an RF retuning delay of the TX chain 218 has a durationthat exceeds the guard interval between an uplink portion 3520 and adownlink portion 3510 of the subframe 3500, the TX chain 218 is switchedindependently from the RX chain 216, and as a result, switching the TXchain 218 to the target component carrier prior to transmission of theSRS symbol 3622 does not interfere with reception of the downlink signal3612. However, switching the TX chain 218 back to the source componentcarrier requires a shortening, or puncturing, or dropping on one or moresymbols, of the uplink signal 3614.

FIG. 37 is a diagram of transmissions that occur in a subframe 3700during an SRS switching operation. In this example, a TX chain 218 ofthe UE 210 is used to transmit both an uplink signal 3614 over thesource component carrier and an SRS symbol 3722 over a target componentcarrier. Hence, the TX chain 218 is switched from the source componentcarrier to the target component in-between transmissions of the uplinksignal 3714 and the SRS symbol 3722. When an RF retuning delay of the TXchain 218 has a nonzero duration, since there is no guard intervalbetween an uplink portion 3720 of the subframe 3500 and a downlinkportion 3710 of the subframe 3700, the TX chain 218 may begin itstransition to the target component carrier prior to start of the SRSsymbol on the target CC. As a result, the uplink portion 3720 isshortened/punctured, on the part that overlaps with the UL RF retuningtime and the SRS transmission.

Carrier aggregation (CA) and carrier selection are techniques thatleverage multiple carriers to increase the effective bandwidth availableto a given mobile device. CA enables multiple carrier signals to besimultaneously communicated between the UE and a supporting basestation, Typically, the UE may be configured with a set of carriers by abase station, such as an enhanced NodeB (eNB). In some instances, thecarriers may be from different frequency bands to add greater bandwidthto support high data rate communications and operations, such asstreaming video or large data files.

Another technology is to rely on carrier switching or selection (CS) toenable the UE to support more carriers than its own capability. Carrierswitching/selection among all carriers available to the serving basestation may allow the UE to access more carriers over time. In thisapproach, component carriers are selected based on several factors, suchas load balancing. While the CS approach generally requiressignificantly less UE enhancement than the CA approach, one drawback toCS is the transition time involved in carrier switching and selection.

During carrier selection, a mobile device may be assigned a set ofcomponent carriers. The base station and/or the mobile device maymonitor the channel quality of each carrier in the assigned set, andtrigger a switch from a current carrier to a target carrier when acriterion is met, e.g., the channel quality of a target carrier exceedsthat of the current component carrier by at least a threshold. As usedherein, the term “current carrier” refers to the carrier that a mobiledevice is transitioning from during a switching operation, and the term“target carrier” refers to a carrier in which the UE is switching toduring a switching operation. Although the target carrier may support ahigher bit-rate than the current carrier, there are nevertheless somelatency and overhead costs that result from switching from the currentcarrier to the target carrier.

The overhead/latency costs may be particularly significant whenbeamformed transmissions are exchanged over the target carrier. Inparticular, it is generally necessary for a mobile device to transmitsounding reference signals (SRSs) over a carrier so that the basestation can derive a complex channel response of the downlink channel,and select appropriate downlink beamforming parameters for the carrier.The downlink channel response can be derived from uplink SRStransmission in a TDD component carrier because downlink and uplinkchannels over the same frequencies are likely to have similar channelresponses due to the concept of channel reciprocity. However, theconcept of channel reciprocity is typically not applicable to differentcarriers, as channel response is typically frequency dependent. As aresult, uplink SRS transmissions over one carrier are generally notuseful in deriving the complex channel response of another carrier.Thus, a mobile device that switches from a current carrier to a targetcarrier may need to perform an SRS transmission over the target carrierbefore a beamformed transmission can be communicated by the basestation. This may introduce latency into the cell switching process.Embodiments of this disclosure provide SRS frame configurations, and SRSswitching techniques, that mitigate the amount of latency associatedwith SRS transmissions when switching from a current carrier to a targetcarrier.

FIG. 38A illustrates a wireless network 3810 for supporting carrieraggregation and/or carrier switching. As shown, a base station 3811communicates with the mobile device 3815 over different componentcarriers 3816, 3817. In some embodiments, the component carrier 3816 isa primary component carrier (PCC), and the component carrier 3817 is asecondary component carrier (SCC). In an embodiment, the PCC carriescontrol information (e.g., feedback from the mobile device 3815 to thebase station 3811), and the SCC carries data traffic. In the 3GPP Rel-10specification, a component carrier is called a cell. When multiple cellsare controlled by the same eNodeB, a single scheduler may perform crossscheduling of multiple cells. In the context of carrier aggregation, onehigh-power node may operate and control several component carriers,thereby forming a primary cell (Pcell) and secondary cell (Scell). AAprimary carrier that is communicated from a base station to a mobiledevice may be referred to as a Downlink Primary Component Carrier (DLPCC), while a primary carrier communicated from a mobile device to abase station may be referred to as an Uplink Primary Component Carrier(UL PCC). A secondary carrier that is communicated from a base stationto a mobile device may be referred to as a Downlink Secondary ComponentCarrier (DL SCC), while a secondary carrier communicated from a mobiledevice to a base station may be referred to as an Uplink SecondaryComponent Carrier (UL SCC). In Rel-11 design, an eNodeB may control botha Macro cell and a Pico cell. In this case, the backhaul between theMacro cell and the Pico cell is fast backhaul. The eNodeB can controlthe transmission/reception of both macro cell and Pico cell dynamically.

In a modern wireless networks, base stations may be grouped together toform a cluster of base stations. Each base station in the cluster mayhave multiple antennas, and may be providing wireless access to multiplemobile devices in a wireless coverage area of the corresponding basestation. Resources may be assigned to the mobile devices based on ascheduling algorithm, e.g., proportional fairness, round robin, etc.FIG. 38B illustrates a wireless heterogeneous network (HetNet) 3820configured to support carrier aggregation and/or carrier selection. Asshown, base stations 3821, 3822 communicate with a mobile device 3825over different component carriers 3826, 3827. The base station 3821 maybe a high-power node (e.g., a macro-cell), and the base station 3822 maybe a low power node, e.g., a pico-cell, femto-cell, micro-cell, relay,remote radio head (RRHs), remote radio unit, a distributed antennas,etc. Accordingly, the base station 3822 may have a smaller coverage areathan the base station 3821. Low-power nodes may provide improvedcellular coverage, capacity and applications for homes and businesses,as well as metropolitan and rural public spaces. FIG. 38C illustratesanother wireless heterogeneous network (HetNet) 3830 configured tosupport carrier aggregation and/or carrier selection. As shown, basestations 3831, 3832, 3833 communicate with a mobile device 3835 overdifferent component carriers 3836, 3837, 3838. The base station 3831 maybe a high-power node (e.g., a macro-cell), and the base stations 3832,3833 may be a low power node, e.g., a pico-cell, femto-cell, micro-cell,relay, remote radio head (RRHs), remote radio unit, a distributedantennas, etc.

Although FIGS. 38B-38C depict base stations communicating with a mobiledevice over different component carriers, it should be appreciated that,in some implementations, base stations in a Het-Net may communicate witha mobile device over the same component carriers.

Some Het-Nets may have multiple high-power nodes and/or multiplelow-power nodes operating over multiple component carriers. Nodes in thesame Het-Net may be interconnected by fast or slow backhaul connectionsdepending on the deployment. Fast backhaul connections may be utilizedto improve coordination between the nodes, such as to effectuatejoint-transmission/reception. Multiple remote radio units may beconnected to the same base band unit of the eNodeB by fiber cable tosupport relatively low latency communications between base band unit andremote radio unit. In some embodiments, the same base band unitprocesses coordinated transmission/reception of multiple cells. Forexample, a base band unit may coordinate a joint transmission (e.g., acoordinated multiple point (CoMP) transmission) from multiple basestations to a mobile device transmissions of multiple cells to aterminal to effectuate a coordinated multipoint (CoMP) transmission. Asanother example, a base band unit may coordinate a joint reception of asignal communicated from a mobile device to multiple base stations toeffectuate a coordinated multipoint (CoMP) reception. Fast backhaulconnections may also be used to coordinate joint scheduling betweendifferent base stations. Densely deployed networks are an extension ofHetNets, and include relatively large numbers of densely deployed lowpower nodes to provide improved coverage and throughput. Denselydeployed networks may be especially well-suited for indoor and/oroutdoor hotspot deployments.

In a wireless network, reference signals, data signals, and controlsignals may be communicated over orthogonal time-frequency resources.For example, the respective signals may be mapped to different resourceelements (REs) in a resource block (RB) of a radio frame. FIG. 39illustrates an embodiment method 3900 for processing signals duringcarrier selection, as may be performed by a mobile device. At steps 3905and 3910, the mobile device processes a primary synchronization signal(PSS) and a secondary synchronization signal (SSS), respectively, todetermine a cell identity and a frame timing of a physical broadcastchannel. At step 3915, the mobile device processes a cell-specificreference signal (CRS) of the physical broadcast channel to obtainchannel information. At step 3920, the mobile device processes aphysical broadcast channel (PBCH) to obtain system information broadcast(SIB) messages for one or more carriers, e.g., SIB1, SIB2, etc. At step3925, the mobile device processes SIB messages to obtain downlinkcontrol information (DCI) associated with the corresponding componentcarriers. The DCI may indicate transmission parameters (e.g., modulationand coding scheme (MCS) parameters, etc.) used to transmit therespective candidate carriers. At step 3930, the mobile device processesCRSs in the candidate carriers to estimate a channel quality associatedwith each of the respective candidate carriers.

At steps 3935, the mobile device performs cell selection based on thechannel quality information derived in step 3930. At step 3940 and 3945,the mobile device begins to monitor the selected carrier and performs arandom access transmission (RACH) uplink transmission to requestresources of the selected carrier be scheduled to the mobile device. Atstep 3950, the mobile device transitions from an RRC_IDLE mode into anRRC_CONNECTED mode. This may be achieved by exchanging messages with abase station associated with the respective carrier.

In some networks, it may be desirable to implement beamforming and cellselection techniques in the same communications session. Before abeamformed transmission can be performed over a time domain duplexed(TDD) component carrier, it is generally necessary for the mobile deviceto transmit sounding reference signals (SRSs) over the carrier so thatthe base station can derive a complex channel response of the downlinkchannel, and select appropriate downlink beamforming parameters. Thedownlink channel response can be derived from uplink SRS transmission ina TDD component carrier because downlink and uplink channels over thesame frequencies are likely to have similar channel responses due to theconcept of channel reciprocity.

However, channel reciprocity is typically frequency dependent, andtherefore uplink SRS transmissions over one carrier are generally notuseful in deriving the complex channel response of another carrier.Thus, a mobile device that switches from one carrier to another may needto perform an SRS transmission over the new carrier before a beamformedtransmission can be communicated by the base station. This may introducelatency into the cell switching process.

One solution to reducing latency during cell switching is for the mobiledevice to perform SRS transmissions over all candidate carriers,including those candidate carriers that are not being used by the mobiledevice. However, in current LTE systems, a mobile device may not bepermitted to transmit uplink SRSs over component carriers if there is adownlink-uplink control channel disparity, e.g., if there are moredownlink control channels than uplink control channels. In particular, anetwork operator may assign more resources to carry downlink traffic andcontrol signalling, than uplink traffic and control signalling, whenthere is a higher demand for downlink traffic, e.g., when more downlinktraffic is being communicated over a given carrier than uplink traffic.

Moreover, some mobile devices may be capable of transmitting SRSsignaling over a limited number of uplink component carriers (e.g., twocomponent carriers) at the same time. Table 1 provides carrieraggregation configurations proposed for 4^(th) generation radio accessnetwork (RAN4) standardization.

TABLE 1 WID BW No. CA Configuration Category Class TDD/FDD Region RELRP- CA_B1_B3_B19_B42_B42 5DL/1UL TDD + FDD Japan R13 151159 RP-CA_B1_B19_B21_B42_B42 5DL/1UL TDD + FDD Japan R13 151160 RP-CA_B1_B3_B7_B7_B28 5DL/1UL FDD Australia R13 151512 RP- CA_41D 3DL/2UL DTDD USA R12 131244 RP- CA_40D 3DL/2UL D TDD China R12 140453 RP- CA_40D(+BW) 3DL/2UL D TDD EU R13 140950 RP- CA_B3_B3_B7_B7_B28 5DL/1UL FDDAustralia R13 151513

The DL-UL CC number disparity can become even more significant withRel-13 eCA which standardized up to 32 DL CCs per UE. Consequently,there could be situations where most of the UE's DL CCs cannot benefitfrom channel reciprocity.

Embodiments that allow mobile devices to quickly switch from one TDDcomponent carrier to another, while still utilizing beamforming, areneeded.

In CA, a UE may be capable of transmitting PUSCH, SRS, RACH, and DMRS on1 UL CC, 2 UL CCs, or even more UL CCs (unavailable as of now). One ofthe UL CCs is configured as PCell for the UE on which the UE transmitsPUCCH, and the other UL CCs, if any, are configured as SCells on whichPUCCH may or may not be supported. The UL PCell and UL SCells may be inthe same band or in different bands, and they may be FDD, TDD, orFDD+TDD, and they may be in the same timing advance group (TAG) ordifferent TAGs. The UE may be configured with more SCells with only DL,and they may be in the same band or in several bands operating in FDD,TDD, or FDD+TDD. Except for the case with only FDD CCs, all of thesescenarios may be considered for SRS carrier based switching. Below tableshows some examples.

TABLE 2 UL UL TDD DL TDD DL TDD DL PCell SCell SCell 1 SCell 2 SCell 3Scenario 1, TDD TDD, none band x band x band x intra-band band xScenario 2, TDD TDD, TDD, band x band x band x intra-band band x band xScenario 3, TDD TDD, TDD, band x band y band z inter-band band x band yScenario 4, TDD TDD, TDD, band x band y band z inter-band band x band xScenario 5, F + T FDD, none band y band y band z band x Scenario 6, F +T FDD, FDD, band y band y band z band x band x Scenario 7, F + T FDD,TDD, band y band y band z band x band y Scenario 8, F + T TDD, FDD, bandx band z band z band x band y

It should be noted that although current RAN4 requirements (such as bandcombinations) do not support some CA configuration scenarios, RAN1design may not be limited to currently supported scenarios.Nevertheless, the network needs to ensure that when operating with SRScarrier based switching, the operations shall comply with RAN4requirements.

To enable fast carrier switching between TDD CCs, a mobile device mayneed to perform SRS transmissions on each candidate component carrier. Amobile device may be instructed to switch from one component carrier toanother by a base station or controller. For example, a mobile devicemay be instructed to suspend its transmission on a first componentcarrier, to switch to a second component carrier, and then to transmitSRS over the second component carrier. The instructions may specify theresources over which to perform the SRS transmissions by indicating anantenna port. The instructions may also identify a timing advance andtransmit power level for the SRS transmissions. The UE may then switchback to the first component carrier. The switching may be alternativelytriggered by dynamic signalling. The network may need to first configurea UE with SRS on all TDD CCs, even if the UE UL CA capability is muchless. Some descriptions will be provided below.

Some general operation designs will be discussed. To facilitate thediscussion, they are categorized into three levels:

The carrier level, concerned with the carrier-level configurations forSRS and switching from one carrier to another, etc.;

The subframe level, concerned with on which subframe the SRS switchingand transmission should be performed and the relation with othertransmissions on that subframe, etc., and

The symbol level, concerned with SRS switching symbols and transmissionsymbols, etc. FIG. 4 illustrates an embodiment SRS carrier basedswitching scheme. As shown, SRS switching is performed on the carrierlevel, subframe level, and symbol level, where D/S/U representdownlink/special/uplink subframes, respectively.

There are several considerations for carrier-level general operationprinciples, requirements, and design. To enable fast carrier switchingto and between TDD component carriers (CCs), the network needs to firstconfigure a UE with SRS on more TDD CCs or potentially even all TDD CCs,even if the UE UL CA capability is much less. Then the UE can switch toand between those carriers and transmit SRS. The switching may beaccording to the network configuration or network indication, includinginformation about the carriers to switch from and to switch to, etc. Thetransmission of the SRS on the switch-to CC is also according to thenetwork configuration or network indication, including the transmissionpower, timing, bandwidth, etc.

During a switching from CC1 to CC2, a UE stops any possibletransmissions on CC1 according to the indicated timing, switches to CC2within a transient period, and transmits a signal according to thecorresponding network indication. After the transmission, the UE mayswitch back to CC1 or switch to CC3 according to the correspondingnetwork indication; this action may be viewed as another switchingaction.

Therefore, a general switching action involves one or more of thefollowing elements: 1) Switching-from CC, the CC the UE is switchingfrom. 2) Switching-from timing, the instance (SC-FDMA symbol location)to break from the switching-from CC. 3) Switching-to CC, the CC the UEis switching to. 4) Transmissions on the switching-to CC, including thesignal formats, contents, resources, timing, power, etc., of thetransmissions on the CC it switches to. 4) Next switching information,such as if the UE should switch back to the switching-from CC, or go toanother CC, or stay in the current CC, etc.

To allow a UE to transmit SRS on more TDD CCs or potentially even allTDD CCs over time, it is necessary to allow SRS to be configured onthese TDD CCs, even if the UE does not support UL CA on all the TDD CCs.This is not allowed in current standards. Therefore, a key standardsimpact is to allow that the number of TDD carriers configured for SRStransmission may exceed the number of carriers dictated by the UE UL CAcapability.

SRS transmissions need to be configured on all TDD CCs. In other words,each TDD CC needs to be configured, explicitly or implicitly by RRCsignalling, with SRS bandwidth configuration, subframe configuration,transmission comb, antenna ports, cyclic shifts, etc. For differenttransmission modes, the SRS density in time may be different, such asprecoding based transmission modes should have higher density of SRS. Inaddition, SRS power control parameters for each TDD CC need to beconfigured.

Some modifications are needed for SRS power control since the currentpower control for SRS assumes the existence of PUSCH on the same CC. SRSpower control configuration without reliance on PUSCH on the same CCneeds to be specified, such as SRS power control parameters similar toPUSCH power control mechanism.

A CC set may be used for simplifying the SRS transmission configuration.A set of collocated CCs in the same band sharing the same set ofantennas corresponding to the same TAG can be configured as one CC set,which may share common properties such as power control parameters,timing advance (TA), pathloss estimate, quasi-co-location (QCL)properties. The method disclosed in 91035003US01 can be adopted hereespecially for SRS configuration purpose. Generally, TDD CCs and FDD CCsare in different sets.

To support SRS carrier based switching, the switching-from carrier andswitching-to carrier may need to be indicated. In some cases, theindication may be explicit such as indicating a switching from CC1 toCC2 in certain signalling, but in other cases, the indication may beimplicit such as when the UE has only 1 CC supporting PUCCH/PUSCH, orthe indication may be implicit such as when the UE has only 1 UL SCellsupporting PUCCH/PUSCH and the UL PCell is not desired to beinterrupted. Furthermore, the explicit indication may be via RRCconfiguration signalling or via physical layer trigger, and theresulting switching and SRS transmission may be periodic or aperiodic.For example, if the UE supports only one UL CC, then it is clear thatthe “switching-from” CC should always be the UL PCell. However, if theUE supports 2 UL CCs, it needs to determine the switching-from CC when aswitching-to CC is specified. The network may configure in such a case,the switching-from CC should always be the SCell and the PCell neverneeds to switch its UL transmission. This is a simple solution, and itmay minimize interruptions on the PCell which generally handles somemore important transmissions (e.g., PUCCH). However, in some situations,it may be desired to switch the PCell as well. One example is there maybe a large number of CCs to switch to, and to solely rely on the SCellUL switching to all other CCs may be inefficient. Another example is, ascurrent RAN4 standards do not support intra-band non-contiguous UL CA,both the PCell UL and SCell UL may switch at the same time to avoidintra-band non-contiguous UL transmissions, which may be preferred overPCell UL muting and SCell UL switching. If the UE supports 3 UL CCs with2 UL SCells (not yet supported in RAN4, though), it needs to determinethe switching-from CC when a switching-to CC is specified. The networkmay configure in such a case, the switching-from CC should always be apredefined SCell and the other SCell never needs to switch its ULtransmission. Alternatively, the network may configure theswitching-from CC should always be SCell1 if the switching-to CC isamong a predefined group of CCs, and the switching-from CC should alwaysbe SCell2 if the switching-to CC is among another predefined group ofCCs or not in the first predefined group of CCs. Alternatively, thenetwork may allow all CCs (or all SCells) with UL to be a switching-fromCC, but which of them will perform an actual switching depends onnetwork signalling, such as a physical-layer signalling transmitted withan aperiodic SRS trigger. In addition, the transmissions on theswitching-from CCs may be punctured or dropped, which will be furtherdiscussed.

In addition, signalling overhead reduction may be considered. Forexample, several TDD SCells may share a common SRS configuration (orrelated SRS configurations), such as antenna ports, aperiodicconfiguration, etc. That is, for some carriers with commoncharacteristics of SRS transmission, the SRS configuration signaling toconfigure the common characteristics to these carriers can beconsidered. This may become especially important if the UE is configuredwith many (up to 32) DL CCs. Designs such as multiple SRS transmissionsover several TDD carriers in one subframe may be considered.

The switching may be according to the network configuration (periodicSRS) or network indication (aperiodic SRS, which also requires RRCconfiguration).

For a “switching back”, if it is not indicated, the UE may stay at theswitched-to CC; or the UE automatically switches back to theswitching-from CC.

One embodiment is to indicate the switching-from CC and switching-to CCexplicitly. For example, a PHY-layer trigger containing (2, 4) defines aswitching from CC2 to CC4. It may imply that after the switching to CC4,the UE will automatically jumps back to CC2. Alternatively, it mayrequire a signalling of (2, 4, 2) for a round trip, or (2, 4) and (4, 2)for a round trip. A sequence of CCs may be indicated, such as (2, 4, 5,6) for switching from CC2 to CC4, then to CC5, then to CC6, or (2, 4)(4, 5) (5, 6) for the same purpose. The combined switching actions canhelp reduce the switching gap overhead. Again, the indication to switchback to CC2 may need to be indicated, or may be implicit. However, if aswitching back is not require for other UL signal transmissions, noexplicit indication of switching back to 2 may mean the UE stays on thelast indicated CC and perform UL transmissions. In one embodiment, theswitching-from CC needs not be signalled explicitly in the triggeringsignalling as it is implicit from RRC configuration signalling whichconfigures each switching-to CC a switching-from CC. It may be allowedthat a switching-to CC is configured with multiple switching-from CC;e.g., CC5 is configured with CC2 and CC1 as the switching CCs. Then theordering may be implicit as CC2 has higher priority to be theswitching-from CC. Alternatively, the ServCellIndex of the CCs arecompared and the one with the highest has higher priority. However, alower-priority CC may be used as the switching from CC if thehigher-priority one is in use and not available, or carrying a signalthat is more important than SRS (e.g., PUCCH, RACH, but PUSCH/DMRS maybe viewed as lower priority, etc.). Without the need of explicitlysignalling the switching-from CC helps reduce triggering signallingoverhead. However, an explicit indication in the triggering signallingmay be supported if the signalling overhead is not considered as a bigissue.

It may be possible that multiple CCs are switching together at the sametime. This may be separately indicated, such as ((2, 4) and (3, 5)),indicating that CC2 switches to CC4 and CC3 switches to CC5 on the samesubframe. However, a preferred embodiment is to indicate ([2,3], [4,5]),which leads to the same operation results but may allow the UE to decideif it performs ((2, 4) and (3, 5)) or ((2, 5) and (3, 4)). In otherwords, there may be an advantage of only specifying the CCs to beswitched from and the final switching outcome without detailing exactlypair of CCs involved in the switching, leaving some flexibility to UEimplementation.

The switching from a CC that can support PUCCH/PUSCH causes aninterruption to the UL transmission on that CC. While allowingsufficient opportunity for SRS switching, the design should strive forreduced negative impacts (such as reduced interruption durations orreduced interruption times) on other UL transmissions, especially forimportant UL transmissions such as PUCCH and PCell transmission.

Moreover, for better sounding performance, interference between SRStransmissions and other UL or DL transmissions needs to be bettercoordinated. This may also impose restrictions on neighboring eNBs' TDDUL-DL configurations.

A SCell DL status may be activated or deactivated. A deactivated CC maystill transmit SRS, so that eNB can monitor the link status, althoughthe transmission periodicity may be longer. However the timing needs tobe ensured. That is, the UE may need to wake up once in a while tomaintain the connection with the deactivated CC, and also send SRS sothat TA may be restricted within a reasonable range. The waking up maybe associated with the DRS transmissions in the DL, such as in thesubframe following the DRS-bearing subframe during a DRS burst, or thenext UL TXOP following the DRS-bearing subframe. In other words, the SRStransmission instances are changed to be aligned with DRS burst,including the periodicity but with an offset of possibly one subframe.

Alternatively, a deactivated CC skips all SRS, since there is no DL,even if the SRS transmission on that CC was preconfigured.

When a CC is activated, it serves as a SRS trigger on that CC (MACtrigger). In current mechanism of SCell activation, a MAC signaling istransmitted from the eNB to a UE, indicating a CC to be activated. TheMAC signaling also serves as an implicit CSI reporting trigger,requiring the UE to report CSI on n+8 subframe and n+24/34 subframe,where n the subframe when the MAC signaling is transmitted. The UE shalltransmit SRS (including SRS switching operation if needed) on n+8 ifconsistent with the UL-DL configuration on the activated CC, or postponeto the next available UL transmission opportunity as indicated by thenetwork. No PHY-layer trigger is needed for this action, and thetransmission is according to pre-configuration. In other words, the MACactivation signaling can serve as a trigger for SRS switching andtransmission. When multiple CCs are activated at the same time, the UEmay need to transmit SRS on the newly-activated CCs possibly on n+8(and/or a later subframe) without PHY-layer trigger, and an ordering maybe configured or standardized for the SRS transmissions. For example,the CC with lowest ServCellIndex shall transmit SRS on the first SRSTXOP, the CC with the second lowest ServCellIndex shall transmit SRS onthe second SRS TXOP, etc. A SRS TXOP is a symbol or a set of consecutivesymbols on which SRS can transmit, taking into consideration ofswitching gaps. Note that a next SRS TXOP may be within the samesubframe of this SRS TXOP or within the next subframe of this SRS TXOP.

The following rules may apply to handling temporary reduction in ULcapability due to SRS transmission. If UE supports n carrier UL CA, whenSRS transmission procedure is ongoing (including retuning periods), UEcan only transmit on n−1 other UL carriers. One carrier needs to have“gaps” during SRS procedure. If UE is not UL CA capable, this would be agap on the PCell. Gap handling may be performed when an UL datatransmission is dropped (and NACKed by network), a DL data transmissionis not received (and UE sends NACK), and/or Network can preventcollision of first UL transmission and SRS transmission.

Given that SRS transmission causes the UE to exceed its uplinkcapability, a procedure is needed to handle the temporarily reduceduplink capability. The starting assumption here is that the UE isconfigured with more UL carriers. Methods for causing a UE to transmitSRS on an SCell are described below.

Case 1: UE does not support UL CA (i.e., only a single carriertransmitted at any time on UL). Case 1 may include one or more of thefollowing steps/features: 1. UE is configured with one or more SCellsthat support uplink transmission; 2. UE is requested to transmit SRS onan SCell; 3. UE retunes from PCell uplink to SCell uplink (furtherdetails on switching in other sections below). UE transmits SRSaccording to SRS configuration provided (in step 2 or prior to step 2).UE retunes from SCell to PCell; 4. The duration in step 3 is consideredan “SRS gap”; 5. During the SRS gap, the following may be true (a) AnyPUSCH transmission UE is supposed to perform is dropped, assumed to havebeen NACKed and a non-adaptive retransmission is scheduled, (b) AnyPDSCH transmission scheduled for the UE is postponed to occur, (c) IfDRX inactivity timer and or DRX retransmission timer are running, theyare suspended when the UE tunes away and are resumed when the UEreturns. The reason for (c) is that DRX inactivity timer can expireduring SRS gap, and UE goes into DRX; if there had not been an SRS gap,the UE may have received PDSCH and stayed in active mode.

Case 2: UE supports n carrier UL CA. Case 2 may include one or more ofthe following steps/features: 1. UE is configured with n or more SCells(i.e., PCell+1 . . . n . . . SCells) that support uplink transmissionand 2. UE is requested to transmit SRS on an SCell #n 3. UE selects anSCell k on which it is going to create an “SRS gap”. It retunes fromSCell k uplink to SCell n uplink, performs SRS transmission and retunesback to SCell k uplink. Note that SCell k can be associated with an RFchain that also supports other SCells. 4. SCell k is chosen using aprioritization scheme with the following features (a) SCell k is chosensuch that SRS gap is caused on the fewest number of activated carriers.(b) SCell k is chosen such that the subframe in which SRS transmissionoccurs is an uplink subframe on SCell k, and there is no uplinktransmission scheduled on SCell k during the SRS gap. (c) SCell k ischosen such that the total power required after substituting SRS onSCell n for the SCell k uplink transmission is no more than the maximumallowed transmit power.

There are several considerations for subframe-level general operationprinciples, requirements, and design.

The SRS has to be transmitted on a UL transmission opportunity (TXOP)indicated by the network, e.g., a UL subframe or the UL portion of aspecial subframe. Unless any other TXOP is introduced and signalled bythe network, the SRS switching has to be consistent with the TDD UL-DLconfigurations on the switching-to TDD carriers. For example, forperiodic SRS switching, the eNB shall ensure that no SRS transmission isconfigured on a DL subframe of a switching-to CC. For aperiodic SRSswitching, the network shall not trigger a SRS transmission on asubframe that will be a DL subframe of a switching-to CC.

For aperiodic SRS transmission on a CC, SRS trigger signalling needs tobe used. The existing signalling and mechanism should be generallyapplicable, though further enhancement and signalling overhead reductioncan be considered.

Designs such as multiple SRS transmissions over several TDD carriers inone subframe may be considered. One aperiodic SRS trigger for SRSswitching and transmission on multiple CCs (takes turns on those CCswith a predefined order, or indicated order such as in the SRS trigger),the multiple CCs may be in a set.

SRS switching signalling may be combined with SRS trigger signalling. Inthe trigger, there may be an indication of the switching-from CC and anindication of the switching-to CC.

Moreover, for better sounding performance, interference between SRStransmissions and other UL or DL transmissions needs to be bettercoordinated. This may also impose restrictions on an eNB's TDD UL-DLconfigurations for different carriers and even neighboring eNBs' TDDUL-DL configurations. As a baseline, the case with fixed TDD UL-DLconfigurations for different carriers and neighboring eNBs should beprioritized. Otherwise, SRS switching subframe may be limited to certainsubframes (e.g, subframe 1 after the subframe 0 DL), or the eIMTAadaptation has to be limited to be consistent with the SRS switchingpatterns. Alternatively, the switching patterns also need to be updatedwith the change of TDD UL-DL configurations (an indicator is senttogether with TDD reconfiguration indicator to indicate the newswitching pattern). Alternatively, periodic or aperiodic SRStransmission on a switching-to CC is dropped. Alternatively, periodic oraperiodic SRS transmission on a switching-to CC is postponed to the nextavailable UL subframe or in general, SRS TXOP. Finally, for aperiodicSRS switching, the network may ensure the consistency so that it wouldnever conflict with the TDD configuration, and the UE shall assume anyaperiodic SRS switching corresponds to an aperiodic trigger alwayscorresponds to an allocated SRS TXOP.

There are various ways to maintain subframe-level consistency.Neighboring eNBs may coordinate with one another such that SRSs arealigned across neighboring eNBs. Neighboring eNBs may coordinate toalign UL-DL patterns and/or GPs. Neighboring eNBs may coordinate and/orcombine CC switching and antenna switching. It may also be helpful toconfigure UEs behavior. For example, the UE may not assume it needs toperform simultaneous UL transmissions on more CCs than its UL CAcapability. If a TDD SCell is indicated by the network for an aperiodicSRS transmission, the UE may interpret that UL transmissions on otherSCells beyond its UL CA capability are dropped or not to be scheduled.If there is a collision between a periodic SRS transmission and anotherUL transmission (e.g., PUSCH/PUCCH transmission on another CC), then theSRS transmission is dropped.

Within a switching subframe, switching times and guard times need to bereserved, possibly before and after the switching operations. This maychange the subframe structures for both the carrier it switches from andthe carrier it switches to. For example, to prevent the switching fromaffecting the next subframe of a TDD carrier, the UE may switch toanother TDD carrier in the middle of a subframe, transmit SRS on theother carrier, and switch back to the carrier some time before theending of this subframe. Due to possible timing differences among thecarriers (especially if they are on different bands), the switching backshould occur early enough during that subframe to avoid any potentialimpact on the next subframe. Therefore, it may not be possible to putSRS on only the last (or even the second to last) OFDM symbol of theswitching subframe. The current standards allow SRS transmission in thelast 6 symbol of a special subframe, but only the last one symbol of aUL subframe which is desired to be enhanced. If SRS transmission isstill on the last symbol(s) of a switching subframe, the next subframemay become a partial subframe. The partial subframe may be in UL or inDL. The partial subframe defined in eLAA may be used here. For example,the next subframe in DL may start at the second slot.

The times needed for switching RF from one carrier to another areexpected to be dependent on the UE's capability and on the bands inquestion. Suppose ‘switching1’ and ‘switching2’ are the durationsrequired for performing the switch in the two directions. FIG. 9illustrates embodiment SRS configurations. As shown, the SRS are placedin a manner that reduces the SRS gap.

Within the SRS placement region (as determined above), the SRS symbolcan be determined based on some pre-specified rule (e.g., the first fullsymbol of the SRS placement region).

In one embodiment, there may be one subframe without any PUSCH/PUCCH,just SRS on several CCs. In other words, the entire subframe may be usedfor several SRS TXOPs. The network indicates the switching orders or SRStransmission orders by one or more UEs. For example, it may indicate theUE with (1, 3, 4, 5) for a subframe, the UE then switches from CC1 toCC3 then to CC4 and CC5 in the subframe. The switching gaps areconsidered, so the SRS on CC3 may be at the 4^(th) and 5^(th) symbols(for different RBs and antenna ports on these 2 symbols), then uses6^(th) and 7^(th) to switch to CC4, transmits SRS on 8^(th) and 9^(th),then uses 10^(th) and 11^(th) to switch to CC5, transmits SRS on12^(th), and switches back on the 13^(th) and 14^(th). Other UEs may beperforming similar operations as well. This may be combined with otherembodiments such as the DL subframe as the switching-from CC or MBSFN onthe switching-to CCs.

A switching-from operation may occur in a UL subframe or a specialsubframe. In the latter case, the switching can occur right after theDwPTS is received. That is, the switching-from action can start at thebeginning of the GP. However, the number of UL subframes and specialsubframes may be limited. To increase the opportunity for switching-fromoperations, an embodiment is to perform the switching-from operation ona DL subframe. If the UE receives no DL grant in a DL subframe, it mayswitch to another CC in the rest of the subframe. For this to be done,it does not require the UE to have additional capability such assimulatenous transmission/reception on aggregated cells. However, if theUE has the capability such as simulatenous transmission/reception onaggregated cells as indicated in simultaneousRx-Tx, the UE may bereceiving DL on the switching-from CC but also switches its UL toanother CC for SRS transmission. Note that the switching-from andswitching-to CCs are generally on different bands for this to work. Theswitching may be a periodic one or for a periodic SRS transmission onthe switching-to CC, in which case the UE may start to prepare theswitching even in the previous subframe (if no UL transmission wasperformed, which may be guaranteed by the network's scheduling actions).The switching may also be triggered by PHY-layer signalling, which theUE received at n−4 subframe or even this subframe, in the latter case,sufficient switching gap needs to be reserved for the UE to switch.

An issue that needs to be addressed is the lack of UL SRS TXOP in theswitching-to CC. Generally, a SRS TXOP lies in a UL subframe or theUpPTS of a special subframe. In a DL-heavy scenario, the number ofconfigured UL subframes and special subframes may be very limited. Theremay even be a TDD CC with no UL or special subframe configured at all.One way to provide a SRS TXOP is to utilize dynamic TDD (eIMTA) featureto dynamically change the TDD UL-DL configuration to allow sufficient ULTXOPs for a switching-to CC. If the network or UE does not support eIMTAor not prefer to use eIMTA for a certain SRS switching, one way out isto indicate certain DL subframes on the switching-to CC as MBSFN. TheMBSFN pattern may be pre-configured, but a MBSFN can still be used forDL transmissions of DMRS-based transmissions if that subframe is notassociated with any SRS transmission. If, however, SRSswitching/transmission is indicated, either a periodic one or anaperiodic one, the network/UE perform the following. Assume UE1 is toswitch from CC1 to CC2 for SRS on subframe n, which is a MBSFN. First,any UE monitoring CC2 still receives the first 2 OFDM symbols of theMBSFN. No UE would detect any DL grant for the subframe and may turn offits monitoring (buffering) for the rest of the subframe (microsleep).UE1 switches from CC1 to CC2, starts to transmit SRS on a symbol asearly as the 3^(rd) symbol (right after the MBSFN PDCCH region) or asymbol later than that, and switch away from CC2 before the subframefinishes. As no UE is monitoring the latter portion of the MBSFN, theSRS would not cause any issue on that CC. To avoid interference to otherCCs in the same band, it may be useful to configure MBSFN and scheduleno UEs on the subframe for all those CCs. The neighboring cells may dothe same, unless the UEs are capable of eIMTA interference mitigation.Effectively, the latter portion of the MBSFN may be all used for SRStransmission/switching. If the UE switches from a MBSFN, it may need toreceive the first 2 symbols and then switch, which may make the firstSRS TXOP x symbols later (x=2, e.g.), if the UE cannot supportsimultaneous transmission/reception on the aggregated CCs; otherwise thefirst SRS TXOP can be immediately after the switching-to CC first 2symbol completes. This has a significant advantage over a specialsubframe or UL subframe as this can provide more SRS TXOPs.

With more TDD CCs configured for SRS than the UE UL CA capability, theUE behavior should be clearly defined. The UE shall not assume it needsto perform simultaneous UL transmissions on more CCs than its UL CAcapability. For example, if a TDD SCell is indicated by the network foran aperiodic SRS transmission on a subframe, the UE shall interpret thatUL transmissions on other SCells beyond its UL CA capability are droppedor not to be scheduled (or based on other rules regarding priorities ofthe transmissions). If there is a collision between a periodic SRStransmission and another UL transmission (e.g., PUSCH/PUCCH transmissionon another CC), then the SRS transmission may be dropped on thatsubframe. In addition, proper collision handling can help reduce theinterruptions on other UL transmission, especially for important ULtransmissions such as PUCCH and PCell transmission.

For example, the SRS switching has to be consistent with the TDD UL-DLconfigurations on the TDD carriers involved in SRS switching. Foranother example, the UE shall not need to perform simultaneous ULtransmissions on more CCs than its UL CA capability. If a TDD SCell isindicated by the network for an aperiodic SRS transmission, the UE shallinterpret that UL transmissions on other SCells beyond its UL CAcapability are dropped or not to be scheduled. If there is a collisionbetween a periodic SRS transmission and another UL transmission (e.g.,PUSCH/PUCCH transmission on another CC), then the SRS transmission isdropped. Priority of carriers and priority of signalling should bedefined.

UE assumption: The UE shall not assume it needs to perform simultaneousUL transmissions on more CCs than its UL CA capability.

One issue that needs to be resolved is the timing advance (TA) of thetransmission, as the UE may not have acquired the TA on the CC. Thisshould not be a problem for intra-band collocated (or QCLed) CCs, astheir timings are associated. However, UL timing may be not synchronizeddue to carrier belonging to an sTAG and no active carriers in the sTAG.If the CC belongs to a TAG with an acquired TA on another CC, the TA maybe used. Otherwise, the UE may not have the TA.

One approach is to ensure that the UE has UL timing on carrier before itperforms SRS transmission. Such an approach may include one or more ofthe following steps. 1. UE receives a request to transmit an SRS on acarrier. 2. UE checks whether it has a timing advance for the carrier.3. If timing advance is current, UE transmits SRS. Otherwise (e.g., TAtimer for the sTAG has expired) UE disregards the request to transmit anSRS.

Another way is the UE needs to use some estimated TA provided by thenetwork or perform RACH. The network identifies random access carrier ofsTAG, perform RACH to obtain timing advance, and then transmit SRS oncarrier. The network may also estimate based on how much time before SRSis transmitted by UE, and how long SRS resource is assigned to UE, whichcan help the network gain a better understanding of the timing of the UEand decision on if a RACH is needed, or which form of RACH is needed.One RACH for one TAG should be sufficient. Consider the case where UE isin a 3DL 1UL configuration. The second and third DL carrier belongs to adifferent timing advance group (TAG) than the first. The second carrierprovides the reference timing and random access opportunities for thesTAG. Such an approach may include one or more of the following steps 1.UE is requested to transmit SRS on carrier 3. The request also providesa RACH preamble; 2. UE determines that it does not have timing advancefor carrier 3 (e.g., TA timer for the sTAG has expired); 3. UE tunesuplink to carrier 2 and performs RACH; 4. UE receives RA response withtiming advance (for carrier 2 and 3); 5. UE tunes uplink to carrier 3and performs SRS transmission.

Alternatively, the UE may need to apply sufficient time gaps before andafter the SRS transmission is needed to avoid interfering with othertransmissions, and the durations of the gaps depend on the possibletiming errors, which is normally at most half an OFDM (or SC-FDMA)symbol duration, but with smaller timing errors, the gaps can beshorter, and the SRS symbol duration can be longer than (such as between1 and 2 OFDM symbol durations). This avoids RACH but essentiallycombines the RACH functionality into the SRS transmission. For example,if the UE needs to transmit SRS on CC2 which it has not TA but thenetwork knows the timing error is within a half OFDM symbol duration,the network can indicate the UE to transmit one symbol SRS on CC2 across2 symbols, with half symbol blanking before and half blanking after. Thenetwork does not schedule any transmissions on these 2 symbols (exceptfor other SRS or RACH). If the time error is only ¼ of a symbol, thenthe blankings can be only ¼ before and after the SRS. In this case thenetwork may indicate the UE to transmit a longer SRS, such as 1.5 symbolduration, which provides more energy for the network to detect. However,SRS of whole symbol durations can always be supported, even though theremay be more blanking. This can also be used for multiple symbol SRStransmissions, such as blanking 0.5 before 2 consecutive SRSs and 0.5after.

After switching from the first component carrier to a second componentcarrier, a UE may cease all transmissions over the first componentcarrier at a time specified by the instruction received from thenetwork. The UE may then switch to a second component carrier within atransition period, and transmit a signal according to the instructionreceived from the network. After the transmission, the UE may switchback to the first component carrier, or alternatively, to a thirdcomponent carrier according to instructions received from the network.

In general, cell switching instructions may identify the currentcomponent carrier, the target component carrier, a time instance inwhich the UE should cease transmission over the current componentcarrier (e.g., an SC-FDMA symbol location), an instance to begintransmitting signalling (e.g., SRS or otherwise) on the target componentcarrier, transmission parameters for the target component carrier (e.g.,signal formats, contents, resources, timing, power, etc.), and/or otherswitching information (e.g., should the UE should switch back to thecurrent component carrier after an interval, should the UE switch toanother component carrier after the interval, should the UE stay in thetarget component carrier after the interval). As used herein, the term“current carrier” refers to the carrier that a mobile device istransitioning from during a switching operation, and the term “targetcarrier” refers to a carrier in which the UE is switching to during aswitching operation.

FIG. 40 illustrates an embodiment SRS carrier based switching scheme. Asshown, SRS switching is performed on the carrier level, subframe level,and symbol level, where D/S/U represent downlink/special/uplinksubframes, respectively.

One goal of SRS switching is to reduce the number of symbol durationsbetween the last transmission over the current candidate carrier and thefirst transmission over the target candidate carrier. Another goal ofSRS switching is to reduce the number of switching operations as well ascombine multiple switching operations. Another goal is to reduce thenumber of collisions between SRS transmissions in order to decrease theSRS processing complexity at the base station and/or mobile device.

A collision may be due to: 1) There are UL transmissions scheduled onCCs more than UE UL CA capability; 2) There are both UL transmission andDL reception scheduled on the same CC at the same time; 3) Theinterruption time due to SRS switching in either UL or DL may cause theUE not able to transmit or receive. Specifically, this may affect notonly the subframe of SRS transmission on a PUSCH-less CC, it may alsoaffect the next subframe of the switching-from CC (e.g., the PCell)during the switching-back operation.

Therefore, if a UE RF switching time is >0 us, and if the SRS on theswitched-to CC is transmitted not early enough, the beginning symbols ofthe next subframe is impacted. FIG. 41 is a diagram of a carrier basedSRS switching scheme. SRS collisions may occur when a UE performs an SRStransmission in the last symbol of a subframe, and another UE needs totransmits or receives a signal in the first symbol of the next subframe.If the SRS symbol position design considers SRS switching time, thensuch collisions may be avoided, or at least mitigated. SRS collisionsmay also be caused by the difference in timing advances betweendifferent UEs (e.g., UEs in different TA groups (TAGs)). Those SRScollisions may be eliminated, or at least mitigated, if the SRS symbolposition accounts for timing advance difference, e.g., if the SRS symbolpositions account for the maximum potential TA differences.

Another goal of SRS switching is to reduce overhead. Each SRS switchingoperation may involve a certain overhead, and frequently switching backand forth can lead to high overhead. The overhead may include signallingoverhead, UE operation overhead, interruptions, etc. It is beneficial toreduce the overhead due to switching. For example, one signalling totrigger more than one SRS switching or SRS transmissions can beconsidered for signalling overhead reduction, and hence the SRS subframemay allow multiple SRS switching operations and transmissions.

SRS switching may include switching from one TDD carrier to another TDDcarrier, switching from a FDD carrier to a TDD carrier, switchingbetween TDD component carriers having different configurations (e.g.,different ratios of uplink-to-downlink resources, TDD special subframes,different guard periods (GPs), etc.).

The switching time affects the SRS subframe. For example, if theswitching time is longer than the GP of a special subframeconfiguration, then it may not be possible to use the first symbol ofthe UpPTS for SRS transmission. If the switching takes up to 2 symboldurations to complete, then the SRS transmission on CC2 may need to becompleted at least 2 symbols before the next subframe starts in orderfor the UE to switch back to CC1, otherwise CC1's next subframe may beaffected.

TA and timing error affect the SRS subframe. There are severalsituations that TA can impact SRS subframe design. For example, if theUE switches from DL reception on CC1 to SRS transmission on CC2, thereneeds to be a sufficient guard time reserved for the CC2 TA before a SRSsymbol can be transmitted. This guard time may be absorbed into the GPin a special subframe, but if CC1 and CC2 are in different TAGs thensome time in addition to the GP may be required. The DL reception on CC1may also be in a DL subframe (e.g., an MBSFN subframe), and a newswitching gap needs to be defined.

For another example, if the UE switches from UL transmission on CC1 inTAG1 to SRS transmission on CC2 in TAG2, the TA difference between TAG1and TAG2 needs to be considered, and there may need to be a guard timebefore or after the SRS symbol(s) on CC2, otherwise sometransmission/reception may need to be dropped. If timing error exists(such as due to timing drift in the UL if the closed-loop timingadjustment for the UL transmissions is not used or has not been used forsome time), the maximum possible timing error may need to added to theswitching gap.

One embodiment SRS subframe may include more symbol positions for SRStransmissions on a target carrier. To avoid affecting any potentialtransmissions/receptions on the next subframe, SRS on a target carriercan be transmitted on a symbol previously not assigned to SRS. In someembodiments, unoccupied symbols (e.g., data, control, etc.) in thetarget carrier can be assigned to carry SRS transmissions.

If RF retuning and TA difference lead to 2 symbol gap for SRS switching,then at more than two symbols (e.g., between two and eleven symbols) maybe assigned to carry SRS transmissions in an UL subframe on the targetcarrier. Similarly, all but the last 2 symbols in UpPTS (includingadditional SC-FDMA symbols in UpPTS) of a special subframe, and symbols4-11 in a DL MBSFN subframe can be used SRS transmissions on the targetcarrier. If more symbols can be allowed for SRS transmission on a targetcarrier, it is more likely to reduce the number of interrupted subframesdue to SRS switching. In other words, for the target carrier,effectively the subframe becomes a SRS subframe, with gaps at thebeginning and at the end to absorb switching time, timing error, and TA,and all symbols in the middle can be potentially used for SRStransmissions.

One embodiment SRS subframe may have multiple SRS switching operationsand SRS transmissions for a UE. To help reduce overhead due to SRSswitching, multiple SRS switchings and SRS transmissions can beperformed consecutively within one subframe. This is made possible byallowing more SRS symbols on a target carrier.

FIG. 42 shows an example of multiple SRS switchings and transmission,all done within one subframe, in which each operation takes 2 symboldurations. Note that on a target carrier, more than one SRStransmissions can occur (e.g., for different antenna ports and/or fordifferent transmission bandwidths). In contrast, if switching operationsare configured or indicated separately and performed separately, thenmultiple subframes would need to be used for SRS switching, leading tohigher overhead.

To avoid interference between SRS and other signals, the SRS subframemay not be scheduled with any other transmissions in the cell (exceptfor the first 2 symbols in the case of MBSFN subframe used as a SRSsubframe and the DwPTS in the case of a special subframe used as a SRSsubframe). Alternatively, if other transmissions in the cell are to beallowed in the SRS subframe, they may be TDMed with the SRStransmission, resulting in truncated transmissions, such as shortenedPUSCH (a partial starting subframe and/or a partial ending subframe maybe used) or shortened PUCCH.

There are several embodiments for the switching subframes.

One embodiment is that the target carrier subframe is a specialsubframe. If the target carrier subframe is a special subframe, allUpPTS symbols may be used for SRS transmission (subject to switchinggaps). However, there are special subframe configurations with only 1symbol UpPTS and not allowing additional symbols to be used for UpPTS(e.g., special subframe configuration 4 with 12 symbol DwPTS); in thiscase the special subframe may not be suitable as a target carriersubframe, and therefore the next two embodiments listed below need to beconsidered.

One embodiment is that the target carrier subframe is a UL subframe. Ifthe target carrier subframe is a UL subframe, all symbols may be usedfor SRS transmission (subject to switching gaps). PUCCH (including theshortened PUCCH format) or PUSCH on the carrier may not be transmittedon this subframe by any UE in the cell unless the SRS occupies a smallnumber of symbols. For example, if the switching gaps and SRStransmissions occur in the second slot of the SRS subframe, other UEs inthe cell may still be scheduled to transmit in the first slot of the SRSsubframe. Alternatively, if the switching gaps and SRS transmissionsoccur in the first slot of the SRS subframe, other UEs in the cell maystill be scheduled to transmit in the second slot of the SRS subframe.If partial PUSCH and/or PUCCH is to be supported, then proper indicationfrom the network should be provided so that UEs transmitting PUSCH/PUCCHcan puncture one or more symbols of the PUSCH/PUCCH transmissionsaccordingly. Puncturing symbols in a transmission may comprise nottransmitting the punctured symbols, or otherwise transmitting nullsymbols (e.g., symbols transmitted at a zero power level), over one ormore resources assigned to carry the transmission. The resources overwhich the symbols are punctured may be a priori information to the basestation and/or UE . . . . In one example, a PUCCH transmission isscheduled to be transmitted in the same subframe as an SRS transmission,and the PUCCH transmission may be shortened in the time domain bypuncturing one or more symbols of the PUCCH transmission that have thepotential to overlap with, or otherwise collide with, symbols of the SRStransmission. However, it may be possible that all SRS transmissionbandwidth is configured to be restricted in PRBs that would not overlapin the PUCCH region. For example, if the bandwidth includes 100 PRBs fora cell, but the eNB configures all UEs associated with the cell with nomore than 94 PRBs and none of the PRBs is in the PUCCH control region,then PUCCH and SRS from different UEs are orthogonal in frequency andmay be sent simultaneously by different UEs (the same UE should not sendPUCCH and SRS on overlapped symbols even if they are orthogonal infrequency). Therefore, a UE may assume that in such a SRS subframe, noSRS from any UE would collide with PUCCH in frequency domain, and the UEis not expected to transmit SRS and PUCCH on overlapped symbols(dropping is adopted if this is to happen).

SRS switching may collide with DL reception. For example, it may impactthe latter symbols of DwPTS (or even DL subframes due to non-alignmentof subframe boundaries for different bands). In this case, overlappingsymbols of PDSCH are punctured. SRS switching is not allowed to impactthe control region of DL; or alternatively, the entire DL transmissionin the subframe is dropped. In one embodiment, the UE assumes thesymbols/slots/subframes that partially or completely overlap with SRSswitching are not to be used for UL or DL transmissions by networkscheduling.

For example, if the first symbol of a UL subframe is affected due to SRSswitching, then the existing shortened PUCCH format may be reused with ashift in time-domain for PUCCH but with the same or shifted RSlocations.

FIG. 43 is a diagram of a carrier based SRS switching scheme. As shown,if UE SRS switching collides with beginning symbols in subframe n+1, ashortened PUCCH carrying A/N for subframe n−k is sent on the unaffectedsymbols in n+1.

In the shortened/punctured PUCCH, the punctured symbols are up to theDMRS symbol, i.e., DMRS symbols should not be punctured. If there is apotential overlap between DMRS symbols and SRS switching, then thepriority/dropping rules apply. For PUCCH formats with x symbols beforethe first DMRS or after the last DMRS, up to x symbols can be punctured.If orthogonal cover code (OCC) is used for UE multiplexing, puncturingmay lead to non-orthogonality. There are a few embodiments for this. Oneis to rely on cyclic shift and FDM only for orthogonality, and no OCC isutilized for orthogonality. For example, with normal CP anddelta_shift=2, ACK/NACK from 18 different UEs can be multiplexed withformat 1a/1b. With more RBs for PUCCH, the capacity should not be a bigproblem. Proper configuration of delta_shift and number of PUCCH RBs canbe helpful. Another is to configure all UEs with the same puncturedPUCCH (with the same number of punctured symbols) to be on overlappingPUCCH RBs, and the OCC is used according to the leftover PUCCH datasymbols. For example, if 3 data symbols are left in a slot, then OCC oflength 3 is used, and at most 3 UEs can be orthogonally multiplex usingOCC. If 2 data symbols are left in a slot, then OCC of length 2 is used.This is similar to shortened PUCCH format 1a/1b which can be reused forthe case that the 1^(st) symbol is punctured.

For the purpose of maintaining OCC orthogonality due to puncturing, theeNB may configure larger PUCCH regions related to PUSCH hopping offsetso that more RBs may be used for PUCCH. And the UE may select n_CCE (orother UE specific parameters) for DCI properly so that the UEs withdifferent numbers of punctured of PUCCH symbols and different formats ofPUCCH use different PUCCH RBs. Alternatively, each mixed format regionmay be used for one type of punctured PUCCH. The unused RBs may also beused and eNB configuration/indication may be needed for this purpose.

Ack/Nack repetition may also be configured by the eNB with a repetitionfactor of 2. The repetition may be used only when a collision withAck/Nack occurs. That is, for subframes not affected by SRS switching,no repetition is used, and for subframes affected by SRS switching,Ack/Nack is repeated, or effectively speaking, delayed to the nextAck/Nack opportunity. The next Ack/Nack opportunity may bundle thosedelayed from the previous opportunity and those for this opportunity.

One embodiment is that the target carrier subframe is a DL subframe. Ifthe target carrier subframe is a DL subframe, it needs to be a MBSFNsubframe, and no PDSCH shall be scheduled. All symbols may be used forSRS transmission (subject to switching gaps). The use of DL subframesfor SRS transmissions may help avoid reducing UL resources and may helpreduce collision with PUCCH.

On the other hand, there are embodiments for the switching-fromsubframes. One embodiment is that the target carrier subframe is aspecial subframe. If the current carrier subframe is a special subframe,the UE can start switching away immediately after DwPTS. In case the GPis sufficient long, the UE may switch back to this carrier for the nextsubframe or for one or more SRS transmissions on this carrier in UpPTS.However, if the DwPTS is long, this subframe is not suitable to be aswitching-from subframe if it would impact the next subframe.

One embodiment is that the target carrier subframe is a UL subframe. Ifa UL subframe is not scheduled with any UL transmission, then thissubframe can be a switching-from subframe. The switching away can startimmediately after the previous subframe or after SRS on this carrier istransmitted. After the UE switches back to this carrier, if there is oneor more symbol left in this subframe, one or more SRS transmissions maybe performed.

One embodiment is that the target carrier subframe is a DL subframe. Ifa DL subframe is a MBSFN subframe and not scheduled with any PDSCH, thenthis subframe can be a switching-from subframe. Immediately after thePDCCH region, the UE can start to switch away from this carrier.

Note that the switching for SRS transmission in the UL may cause DLinterruption. The DL interruption may be due to the RF retuning in theUL switching, and in this case, the DL interruption caused by the ULretuning is no longer than the RF retuning time (e.g., 2 symbols). Thismay be the case if the UE has an implementation with a single RFIC orstrongly coupled transmission and reception chains. If the UE reports aninterruption is needed for CA operations (e.g., CAactivation/deactivation, etc.), then it is possible that DL interruptiondue to UL retuning would occur, otherwise the DL interruption due to ULretuning would not occur. Alternatively this may be a UE capabilityreported to the network reflecting RF retuning time and whether DLinterruption would occur during RF retuning. For SRS transmission on atarget carrier, during the transmission the DL may also be interruptedif the UE is not capable of simultaneous reception and transmission inthe aggregated cells. The interrupted DL symbols or subframes need to behandled, such as occurring in blank portion of a MBSFNMBSFN subframe. Ifthere are multiple possibilities of which carrier(s) will be interruptedin DL, needs to specify the DL carrier(s) of interruption. Theinterrupted DL carrier(s) may be viewed as the switching-from CC(s) fora SRS switching. For example, if a switching occurs in subframe n, andsubframe n+1 is affected, and subframe n+1 is a DL subframe, either CC1or CC2 may be selected as the affected DL subframe. The network canconfigure or indicate which one should be selected.

The above current carrier subframe types and target carrier subframetypes can be combined. It is more likely that in typical operations, thecurrent carrier subframe type and target carrier subframe type are thesame, but in FDD+TDD CA, inter-band CA, etc., other cases can happen.Note that when both the switching-from and target carrier s areconsidered, the SRS transmission symbol positions are not only affectedby the subframe types but also the RF IC architecture of the UE. Forexample, if the transmission and reception of the UE is done by one RFchain or they are tightly coupled, then fewer symbols may be used forSRS transmission; otherwise more symbols may be used for SRStransmission. These are illustrated in FIG. 42. Some more details aredescribed below.

In FIG. 44A, it shows the case that the UE switches from CC2 to CC1 forSRS transmission on CC1 in a SRS subframe. Both carriers are specialsubframes. The UE is assumed to have single RF design so that thetransmission and reception on the CCs are coupled. It is also assumedthat the special subframe configurations are aligned, i.e., thedurations of DwPTS and UpPTS are the same for the CCs. Then the UE needsto monitor the DwPTS in DL, and starts the switching after the ending ofthe DwPTS. However, if the UE detects no PDSCH scheduled for thesubframe, it may start the switching immediately after the controlregion ends. For example, if the control region has 2 symbols but theDwPTS has 3 symbols, then the UE may start switching from the 2^(nd)symbol (counting from 0) if it does not detect any grant for PDSCH andknows it needs to switch to CC1. However, the DwPTS may contain more CRSafter the control region. In legacy systems, the UE may or may notmonitor those CRS if there is not PDSCH. This may be kept, but a betterway may be to allow the UE not to monitor those CRS so that a switchingcan occur earlier in time. The network may configure the UE to transmitSRS on CC1's symbol 4 while the control region spans symbol 0 and 1 andthe UE needs 2 symbols to switch, even if the DwPTS has, say, 9 symbols.That means the UE should not expect a PDSCH grant, and it can ignore allCRS after the control region but switches to CC1 immediately after thecontrol region. Another alternative is that if the UE is configured totransmit SRS on CC1 on an early-enough symbol (say, symbol 4), then theUE may assume the subframe contains no grant to it to detect and it doesnot need to monitor CRS either on CC2. In that case, the eNB would nottransmit any information to the UE to receive in that subframe. There isalso a case that the eNB sends aperiodic SRS trigger a few subframesbefore to the UE to schedule SRS transmission on CC1, and the UE maybehave similarly. If same subframe trigger is used, then the UE shoulddetect the PDCCH in the control region, and if such a trigger is found,then no other DL reception is expected, and the UE can immediatelyswitch away from CC2. Note that there may be some time for the UE todetect the PDCCH for the trigger, so the eNB shall not trigger a SRStransmission on a symbol too early for the UE to transmit. For example,if the control region has 2 symbols, and the UE takes one symbol time todetect and decode the PDCCH (if the UE capability is known to thenetwork), then the earliest switching can occur at symbol 3, and theearlier SRS transmission can occur at symbol 5 on CC1. After theswitching, the UE may start the SRS transmission per configuration andindication, including the symbol positions. Note that there may (or maynot) be a gap of symbol(s) before the signalled SRS transmissions. Theremay be one or multiple SRS transmissions on CC1, and the UE may besignalled to switch to yet another CC for SRS transmission if there issufficient time in the subframe left. Finally, the UE may be scheduledto transmit SRS in UpPTS (on one or two or more symbols) on CC2, so theUE would switch back to CC2 and transmit. If carrier switching tosupport RACH transmission is also performed, similar concepts andprocedures can be adopted.

Similar embodiments may be used for FIG. 44B, where the special subframeconfigurations are different for CC1 and CC2. But in any event, the UEcan switch away from CC2 after it completes the DL reception. Thevarious embodiments discussed above can be adopted for this case.Needless to say, if there is not enough time left on CC2 in UpPTS, thena SRS transmission on CC2 should not be performed as shown in thefigure. In FIG. 44C, the same settings as in (a) are assumed except thatthe UE is assumed to have separate/decoupled transmission and receptionRF design, so that the UE can freely switch its transmission from CC2 toCC1 anytime as long as no UL on CC2 is scheduled. Therefore, in thefigure, the UE still receives DL for the entire DwPTS, but the UL isswitched to CC1 even before the DwPTS ends. The UE may switch the ULeven earlier, if the UE knows that SRS switching is to be done in thissubframe. For example, if the SRS transmission on CC1 is configured,then the UE can switch even before the subframe starts. For anotherexample, the DwPTS region may span 10 symbols, but the UE detectstrigger for SRS transmission based on PDCCH in symbols 0 and 1 andcompletes the detection and decoding of DCI in symbol 2, then it canstart switching on symbol 3 while the DL reception is still ongoing tillsymbol 9. However, in this case, the UE needs to report its RFcapability, such as capable of simultaneous reception and transmissionin the aggregated cells.

FIG. 44D shows a similar example as (c) but the special subframeconfigurations are different for the CCs. Similar embodiments can beadopted. FIG. 44E shows an embodiment of switching from a UL subframe toa UL subframe. CC2 cannot be scheduled with any UL transmissionoverlapping with CC1's SRS transmission and the switching time. However,on non-overlapped symbols, SRS and shortened PUSCH may be transmitted onCC2 (see FIG. 44F for an example).

FIG. 44G shows an embodiment of switching from a DL subframe to a DLsubframe. Both subframes are configured as MBSFN. Several other casesare shown in FIG. 441, FIG. 44J, and FIG. 44K, but it is not meant to beexhaustive. Above embodiments apply whenever appropriate, andcombinations of them can be done.

The switching-from and/or switching-to subframe may also be a DRSsubframe or immediately after a DRS subframe, especially if the carrieris in deactivated mode or the UE is in DRX.

If RACH is to be transmitted, similar designs follow.

The switching gap affects the SRS subframe, from efficiency point ofview and feasibility (in terms of currently supported SRS symbolpositions) point of view.

For example, if the switching gap (e.g., 900 us) is longer than theduration of GP and UpPTS of a special subframe configuration, then itmay not be possible to use the any symbol of the UpPTS for SRStransmission. In this case, the next subframe, which is generally a ULsubframe, has to be used for SRS transmission. Clearly, relying on onlythe last symbol of the UL subframe as currently supported is far fromefficient.

For another example, in the case that a UE switches from CC1 to CC2 forSRS transmission on the last symbol of a UL subframe, and if theswitching gap takes a non-zero time to complete, then when the UEswitches back to CC1, CC1's next subframe will be impacted. If it isdesirable to reduce the number of subframes impacted by SRS switching,SRS transmission opportunities supported by current UL subframes areinsufficient.

For yet another example, if the switching gap is long, say 500 us ormore, then the switching-back action on a special subframe will impactthe next subframe, even if the SRS transmission is on the first symbolof UpPTS.

To summarize, one can see that if all RF switching duration values aresupported in the standards, then the current SRS symbol positions inspecial subframes or UL subframes are insufficient. There are twoalternative choices:

Choice 1: Add more SRS transmission opportunities; or

Choice 2: Support all RF switching durations provided by RAN4.

If Choice 2 is decided, then some RF switching durations provided byRAN4, e.g., 500 us, 900 us, will not supported at least in Rel-14,though future releases may provide support for them.

Alternatively, if Choice 1 is decided, RAN1 needs to standardize new SRStransmission opportunities in addition to the up to 6 symbols in UpPTSand the last symbol in UL subframe. The rest of the contributionprovides more details for this choice.

With Choice 1, all SRS switching gaps need to be supported. Inevitably,SRS switching operation will span more than one subframe, especially forthe cases with long switching gaps. For efficiency, it is preferred toallocate multiple consecutive subframes for SRS switching. For example,one complete SRS switching operation (from switching from CC1 tillswitching back to CC1) can contain a special subframe, the next ULsubframe, and possibly even one more subframe. The UE can performmultiple SRS transmissions on one or more TDD CCs in these subframes.Note that those TDD CCs may lie within one band and there may be noswitching gap between the SRS transmissions on those TDD CCs.

Next we consider options for timing advance for SRS on TDD CCs withoutPUSCH.

A UE may have more TDD CCs with PDSCH than TDD CCs with PUSCH. Withproper network configurations and indications, UE can perform switchingto any TDD CC and transmit SRS on that CC. One problem that needs to beresolved is the timing advance (TA) of the transmission, as the UE maynot have acquired the TA on the CC. Note that in previous releases, a CCwithout UL may not be configured in any TAG. At least for SRS switchingpurposes, any CC that will support SRS transmission needs to beconfigured in a TAG. To do so, the eNB needs to configure a UE with TAGsand add the indexes of all CCs supporting PUSCH/PUCCH/SRS/RACH intocorresponding TAGs.

There are two main cases to be considered:

1) If the CC belongs to a TAG with a valid acquired TA on another CC ofthat TAG, the TA may be used as already defined in the standards.

2) If the CC belongs to a TAG with no valid acquired TA on any CC ofthat TAG, there are again two cases:

a) At least one CC in the TAG supports PUSCH. In this case, the reasonthat the TAG does not have a valid acquired TA may be that there is noRACH or TA update for an extended period of time. Then RACH on the CCwith PUSCH can be used to acquire the TA, or current TA update mechanismcan be used on that CC. The network should ensure that before SRSswitching to a CC without PUSCH in the TAG, a valid TA is available forthe TAG. For example, before the eNB sends a SRS trigger for a CC, theeNB needs to make sure that the UE has a valid TA for the associatedTAG. So from UE point of view, the UE may assume that the eNB would notsend a SRS trigger for a CC without a valid TA associated with the CC'sTAG. One embodiment is that when the UE receives an activationsignalling for a CC in a deactivated TAG with PUSCH and RACH (possiblyon a second CC), the UE should transmit RACH. This RACH can benon-contention based, and the time-frequency resources for the RACH maybe indicated in the activation signalling. Or alternatively, the UEshould not transmit the SRS, and the UE may send a request (e.g.,scheduling request) to the eNB to request for a RACH on a CC supportingRACH in the TAG.b) No CC in the TAG supports PUSCH. This is the main focus of thiscontribution. There are a few options:i) Option 1: Introduce RACH on One of the CCs in the TAG.

This requires standards changes including the following. First, thestandards should allow a UE to be configured with RACH on more CCs thanits UL CA capability, but on those CCs, no PUSCH is configured.Pre-configuration of the transmission resource/preamble code group ofnew RACH, and employing the PDCCH on the current carrier to trigger thetransmission of preamble code in these pre-configured resources on theswitched-to carrier could be considered. Second, collision between RACHon a PUSCH-less CC and other UL transmission on another CC may occur ifthese UL transmissions exceed the UE UL CAP capability, and hencecollision handling for the newly introduced RACH needs to be provided.The collision handling is similar to SRS collision handling, but theRACH may have higher priority than SRS to ensure the timing isavailable. In general, the RACH may have higher priority than any otherUL transmissions except for PUCCH carrying ACK/NACK. Alternatively, theRACH may follow the same priority as the aperiodic SRS switching. Third,this RACH may be non-contention based and may be used to acquire atiming advance on a carrier that does not include a physical uplinkshared channel (PUSCH). Fourth, considering carrier switching time ofpossibly a couple of symbol durations, the shortened RACH preambleformat 4 may be used. The RACH is also subject to the switching timelimitations, so it may take the UE a couple of symbols to switch to aTAG for RACH transmission, and then switch back within another 2symbols. If the shortened RACH is used in the UpPTS, then the nextsubframe may be impacted and the UE cannot receive DL or transmit in ULon the switching-back carrier. Then the next DL may become a partialsubframe, or the next subframe may become an UL subframe withoutscheduling any UL transmission on the switching-back carrier by the eNB.In other words, if RACH with shortened form is to be performed in UpPTS,then the next subframe may be UL and without any scheduled transmissionson the carrier. Similar concepts can be adopted for regular RACH.Alternatively, the network may indicate the UE to transmit RACH at least2 symbols (or another appropriate amount based on the needed switchingtime) before the subframe ends. This requires the shortened RACH to beshifted away from the last 2 symbols of the special subframe (RACHsymbol position should be configured and/or indicated), and regular RACHto be shortened in time domain and leaves sufficient gap before thesubframe ends. Non-shortened RACH formats (e.g., format 0), if theswitching times plus transmission time can be fit into a subframe, canalso be supported. For format 0, the RACH transmission time is about 900us, so a switching of less than 40 us should work and no other subframewould be affected. For one TAG, one RACH on a carrier in the TAG issufficient. RACH would not be needed afterward if SRS transmissions inthe TAG keep the UE updated with TA adjustment. Therefore, such RACH maybe only an initial RACH after serving cell configuration, or after a TAGis activated after deactivation or long DRX. However, as RACH is usuallyneeded only once for a TAG, even if the RACH may collide with othersubframe's transmission/reception, this may be acceptable and in thesecases, RACH has higher priority and other transmissions are dropped. Thenetwork should have the knowledge beforehand and may scheduleaccordingly to avoid the dropping. The UE may assume no othertransmissions/receptions would occur if they collide with RACH.

For the RACH configured on TDD CCs without PUSCH, the UE needs toperform carrier switching. The switching-from CC needs to be specifiedif the UE supports more than one CC, in RRC configuration for RACH or inDCI for triggering the RACH. For periodic SRS, it is preferred toconfigure the switching-from CC in RRC configuration. For aperiodic SRS,the switching-from CC may be configured in RRC configuration, oralternatively, specified in PDCCH order for triggering the RACH.Alternatively, as a default, if the UE support only 2 UL CC CA, theswitching-from CC for RACH is always the UL CC not associated withPCell, i.e., PCell UL is not impacted. One example is that CC 1 isswitching-from carrier while CC 2 is switched-to carrier. The new RACHtransmission could be configured and/or indicated in CC 1, and themessage 1 is sent in CC 2 followed by message 2 response in CC 1 or CC2.

Thus, the network can configure non-contention-based RACH on PUSCH-lessCC for only one CC in a TAG group without PUSCH, with new configurationssuch as switching-from CC specified, cross-carrier scheduling of RACHspecified, RAR content specified, etc. RACH format 4 should be supportedand shifted earlier for non-zero switching time UE so that the nextsubframe is not affected. Collision handling reuses existing ones forRACH, or follows the rules for SRS switching.

TA adjustment via TA MAC CE can be done based on SRS transmissions. Thecurrent support can be used as a baseline. Cross-carrier indication forTA commands may need to be supported. For example, the TA command may becarried on CC1 though it is to be applied for CC2 (or more generally,for the TAG where CC2 is in).

ii) Option 2: UE Estimates TA.

UE can estimate TA for TAG2 based on TA for TAG1 (associated with thepropagation delay between the UE and cells in TAG1) and DL arrivaltiming difference between TAG1 and TAG2 (associated with the propagationdelay difference to cells in TAG1 and to cells in TAG2). The timesynchronization error between TAG1 and TAG2 will lead to some error tothe TA estimate for TAG2, but for TDD cells serving the same UE, thetime synchronization error is small (e.g., <500 ns).

The UE then transmits SRS after switching to the CC with the estimatedTA, say, on symbol n. However, due to estimation error in TA, the SRSmay partially overlap with the symbol before it (symbol n−1) and afterit (symbol n+1). There are again a few cases:

a. If the eNB does not schedule any other UE on the CC except forpossibly SRS, then the overlap will not impact any PUSCH/PUCCH, since asdiscussed before, the SRS symbol position may lie in the middle of theSRS subframe.

b. If the eNB schedules another UE for SRS transmission on symbol n−1 orn+1, the SRS transmissions from the UEs will partially overlap in time,but both SRS transmissions can be detected by the eNB since the SRS isrepeated (i.e., redundant) in time domain associated with the combstructure in frequency domain. The overlap may nevertheless cause somedegradation of received SRS, so it is up to the eNB to determine if SRSfrom another UE may be scheduled or not.c. If the eNB schedules another UE for SRS transmission on symbol n, theSRS transmissions from the UEs should have cyclic shifts far from eachother, such as one uses cyclic shift 0 and the other uses cyclic shift4.

To summarize this option, UE can estimates TA and transmit SRS on aswitching-to CC. Proper eNB implementations can ensure the SRS to bedetected by the UE. No standards impact is required for the option, butsome RAN4 testing of UE TA estimation may be needed.

iii) Option 3: UE Estimates TA and Applies Extra Guard Times.

This is similar to Option 2, but the UE leaves some gaps as guard timesfor the SRS transmission, so that even with some TA estimation error,the SRS would not overlap with the symbol before it or after it.Therefore, there will be any issue if the symbol before or after the SRStransmission is scheduled for other transmissions. To do so, theeffective SRS transmission in timing domain is shortened, or 2 symbolsare combined for one SRS transmission in the middle of the 2 symbols.This option requires some standards changes.

If DL timing difference between TAGs is significant, e.g., more than afew microseconds but up to about 32 us between a FDD TAG and TDD TAG,and UE knows only FDD TAG TA but not TDD TAG TA, then purely relying onUE estimate of TA for the TDD TAG may result in larger error. However,such an error is bounded by two times the DL transmission timingdifference plus propagation time difference. In typical cases, this isbounded by 1 symbol duration. If the eNB can blank one symbol before andone symbol after the SRS transmission symbol(s) by a UE, then nocollision/interference would be incurred, and the eNB can rely onsearching in time domain to recover the SRS. This is similar to thevariable duration RS design described in U.S. patent application Ser.No. 14/863,382 entitled “Device, Network, and Method for Communicationswith Variable-duration Reference Signals,” which is incorporated byreference herein as if reproduced in its entirety. Alternatively, eNBcan signal the UE about DL timing differences between 2 TAGs. Thesignalling may be in the form of TA or TA adjustment. In other words,although the eNB may not have received any signal (RACH or SRS) from aUE on a TAG, it may still send TA signalling to the UE regarding a TAG,and the TA command is actually the difference between the transmissiontiming difference between the TAGs (possibly plus some other smalladjustments provided by the eNB). Alternatively, the network canconfigure a TA for a TAG without any PUSCH/PRACH/PUCCH, and the TAreflects the transmission timing difference between the TAG and PCellTAG. At the UE side, it receives the TA, but the TA is a relative valueto the PCell TA. Alternatively, the TA configured to the UE may be arelative value to the TAG's DL reference timing, and then the UE shouldadjust its TA relative to the TAG's DL reference timing. The UE mayestimate report the DL receiving timing difference to the eNB. It mayuse the difference to estimate the TA by TA2=TA1+delta_DL−delta_Tx,where TA1 and TA2 are TAs of the 1^(st) and 2^(nd) TAGs, delta_DL is theDL receiving timing difference (TAG2 DL receiving time minus TAG1 DLreceiving time), delta_Tx is the eNB DL transmission timing difference(TAG2 DL transmission time minus TAG1 DL transmission time). Such aformula may also be used by the eNB if all information is available.

Next we discuss periodic SRS and aperiodic SRS designs. It is generallyaccepted that aperiodic SRS transmission provides the highestflexibility for the network to obtain channel quality information basedon sounding. Therefore, switching to a TDD carrier without PUSCH toperform aperiodic SRS transmission may occur.

Aperiodic SRS is configured via RRC signalling and triggered dynamicallyvia DCI formats 0/1A/2B/2C/2D/4 for TDD and 0/1A/4 for FDD. Theconfiguration and DCI may be enhanced to support SRS transmission basedon carrier switching. For example, the DCI may indicate a SRStransmission on one or more carriers, including those without PUSCH.Therefore, the carrier ID associated with the SRS transmission may needto be included in the DCI. If the SRS symbol position needs to beindicated (e.g., the SRS transmission starts at symbol x and ends atsymbol y, or starts at symbol x and lasts z symbols, for a particularSRS transmission), such information can be included in the DCI. The DCImay schedule other transmissions or receptions for the carrier receivingthe DCI or for another carrier, but the scheduled carrier may be thesame as or different from the carrier(s) triggered for SRStransmissions. In cases that the indicated SRS transmissions conflictwith the other transmissions indicated by the same (or a different) DCI,collision handling mechanisms are provided. To avoid collision due tothe same DCI used for both SRS switching triggering and scheduled UL orthe Ack/Nack from the scheduled DL, the timing relation between the SRStriggered switching may be changes (such as shifted to the next SRStransmission opportunity) or the DCI for SRS triggered switchingrequires a separate DCI.

The carrier ID associated with the SRS transmission may need to bespecified in the DCI explicitly or implicitly (via association with oneof the multiple parameter sets configured via RRC signaling). Thisimplies that cross-carrier triggering of aperiodic SRS can also besupported. More particularly, a DCI sent on CC1 may be used forcross-carrier scheduling of data for CC2 and cross-carrier triggering ofSRS transmission on CC3.

Regarding the number of parameter set configured for aperiodic SRStransmission, the current specification supports up to 3 parameter setsvia 2 bits in DCI format 4. If the 2-bit trigger becomes insufficient,one more bit could be considered to be added. On the other hand, foreach DL CC (include each FDD CC if aggregated), there can be up to 3parameter sets configured, which could lead to in total a sufficientlylarge number of parameter sets usable for aperiodic SRS. Note that theDCI sent on a FDD carrier to trigger the SRS transmission(s) on aPUSCH-less TDD CC may also be allowed. In other words, two options maybe considered: either increasing the number of SRS request bits orsupporting carrier-specific SRS parameter set configuration. Similar tothe introduction of carrier-specific SRS parameter sets, which utilizesthe carrier dimension to carry more information about the selection of aparameter set without explicit bits in DCI, one could use otherdimensions as well for this purpose. For example, if the trigger is sentin a DL grant, then the indication is associated with a group ofparameter sets for DL grant. Otherwise, if it is sent in a UL grant,then one in another group of parameter sets is indicated. Likewise, thiscan further utilize the DCI format dimension, that is, for0/1A/2B/2C/2D/4 for TDD and 0/1A/4 for FDD, each format of each TDD/FDDconfiguration may have a format-specific parameter set. The subframenumber (or slot number) within a radio frame or subframe type (DL orspecial subframe) may also be utilize similarly. For example, a triggersent at subframe 0 and a trigger sent at subframe 1 may both lead to SRSswitching in subframe 6, but if the former is used, the UE uses a firstparameter set, while if the latter is used, the UE uses a secondparameter set.

The switching-from CC may need to be specified for each transmission.One way is to specify the switching-from CC in RRC configuration ofparameter sets. Another way is to specify in the DCI trigger. The formerhas less physical-layer signalling overhead, but it is less flexiblethan the latter. RAN1 may consider the pros and cons and decide which tobe supported.

For enhanced efficiency, SRS switching operations for several SRStransmissions can be configured to be contiguous in time (subject to SRSswitching gaps). This requires the aperiodic SRS to support multipleconsecutive SRS transmissions (on the same or different CCs), andhigh-layer signalling to configure one or more SRS configurations atonce, and DCI trigger to trigger one or more SRS transmissions at once.For example, the first SRS configuration is for SRS transmission on TDDCC1 in OFDM symbol k, the second SRS configuration is for SRStransmission on TDD CC2 k+1, and so on, and if the associated bit isset, then the UE will perform carrier switching multiple times andtransmit SRS on the specified CCs accordingly.

If the SRS symbol position needs to be indicated, such information canbe included in the DCI.

In case that the indicated SRS transmissions conflict with the othertransmissions indicated by DCI in a subframe (said, subframe n),collision handling mechanisms should be defined. For example, atsubframe n+4, the ACK/NACK for the DL transmission in subframe n needsto be transmitted, and other UL transmission (e.g., PUSCH, CQI feedback)needs to be transmitted in subframe n+4 based on the DCI in subframe n.In this case, the SRS transmissions associated with the SRS trigger insubframe n should not occur in subframe n+4. It may be postponed to thenext SRS transmission opportunity, until no DL or UL grant is sent tothe UE in subframe n. Several alternatives may be considered. First, theSRS transmission may be postponed to the next aperiodic SRS transmissionopportunity, and the next aperiodic SRS transmission opportunity may beassociated with no operation (for transmission or reception) ascoordinated by the eNB, or the next aperiodic SRS transmission is alwaysassociated with UpPTS where no ACK/NACK can be sent. Second, DCI for SRSswitching may be associated with no other scheduled DL/UL transmission.Third, in the case FDD+TDD CA, FDD and TDD may have different timingrelationships, and thus the DCI for SRS in FDD CC may not causecollision to following UL transmission. Fourth, different HARQ timingfor other transmissions scheduled in the SRS trigger may be defined. Ifaperiodic SRS switching is restricted to special subframe UpPTS (e.g.,forming a 10-ms periodicity SRS switching pattern or 20-ms periodicitySRS switching pattern), it could avoid many of the potential collisions,especially to Ack/Nack. In this case, the periodic SRS and aperiodic SRShave similar behavior, and the trigger may be omitted. Alternatively,the trigger is to provide additionally information (e.g., SRS parameterset selection) for periodic SRS. Therefore, it is needed to specify SRStransmission opportunity (subframe position and symbol position).

Periodic SRS has been supported in LTE since Rel-8 as the main means foruplink sounding. Though periodic SRS is viewed as not as flexible asaperiodic SRS, periodic SRS is associated with less signalling overheadthan aperiodic SRS, and due to its predictability of occurrence, it maybe easier for collision avoidance and handling. With properconfigurations, periodic SRS may be utilized more efficiently thanaperiodic SRS in certain scenarios. In addition, periodic SRS may beconfigured with relatively long periodicity (e.g., 20 ms or longer,especially if the switching gap is long) and/or associated with lowerpriority during collision, so that periodic SRS switching may not affectother transmissions. The configured SRS transmission should also avoidcertain subframes, such as subframes 0 and 5. Therefore, periodic SRStransmissions may be used for SRS carrier based switching.

The configuration of periodic SRS can use existing mechanism andsignalling as the baseline. For enhanced efficiency, SRS switchingoperations for several SRS transmissions can be configured to becontiguous in time (subject to SRS switching gaps). This requires theperiodic SRS configuration to allow multiple consecutive SRStransmissions (on the same or different CCs), and high-layer signallingto configure one or more SRS configurations at once. For example, thefirst SRS configuration is for SRS transmission on TDD CC1 in OFDMsymbol k for bandwidth configuration 1, the second SRS configuration isfor SRS transmission on TDD CC1 in OFDM symbol k+1 for bandwidthconfiguration 2, and so on. That is, multiple consecutive SRStransmissions on the same CC may be for different bandwidthconfigurations, antenna ports, and so on. Multiple consecutive SRStransmissions on several CCs may also be configured. For example, thefirst SRS configuration is for SRS transmission on TDD CC1 in OFDMsymbol k, the second SRS configuration is for SRS transmission on TDDCC2 k+1, and so on.

It is needed to configure SRS transmission opportunity (subframeposition and symbol position) for periodic SRS, and the configurationshould take into account of switching time to reduce the impact to othertransmissions. For example, if the switching time is nonzero, theconfigured SRS symbol position should avoid the last symbol of asubframe.

An issue with periodic SRS is that, if the SRS is rather frequent, itmay incur high overhead and cause many disruptions to normaltransmission/reception. One way out is to focus onrelatively-long-periodicity SRS for SRS switching (e.g., 20 ms orlonger), especially if the switching gap is long. For more short-termsounding, the network can rely on aperiodic SRS. In this case, thelong-periodicity SRS switching should have relatively high priority. Forexample, the priority of 40 ms periodicity SRS switching may have higherpriority than other UL transmissions (except for possibly those carryingAck/Nack). Note that even if the Ack/Nack is designed as of lowerpriority, this generally would not cause any problem as the eNB canschedule accordingly beforehand so that no Ack/Nack needs to be collidewith the long-periodicity SRS. Another way is to allow short-periodicitySRS for SRS switching, but the priority is low, so that its disruptionto normal transmission/reception can be reduced. When a long-periodicitySRS collides with a short-periodicity SRS, the short one may be dropped.

A preferred resource for periodic SRS switching/transmission is thespecial subframe UpPTS. One embodiment is 20 ms periodicity, forsubframe 1 (or subframe 6 for configuration 0/1/2/6).

For a deactivated carrier or a carrier in DRX, periodic SRS is nottransmitted according to current standards. SRS carrier based switchingshould also follow the same principle, i.e., a UE will switch to aPUSCH-less TDD carrier for SRS transmission only if that carrier isactivated and in Active time. This also helps reduce SRS switchingoverhead. When the UE is in DRX and/or deactivated, then no periodic SRSwould be transmitted. However, aperiodic SRS may still be transmitted.

It may also be possible to support periodic SRS switching only, since asseen above, periodic SRS and aperiodic SRS may be configured and usedvery similar to each other.

General Assumptions and Considerations for Collision Handling

The switching time is reported by UE as a part of UE capability; knownby UE and eNB. The report may be indicating one or more of the followingvalues: 0 us, 30 us, 100 us, 200 us, 300 us, 500 us, 900 us. Not allvalues may be supported for SRS switching, especially for longerswitching times. The reporting may be for each pair of CCs, but theoverhead would be high. In general, the UE may only need to report a fewcategories of switching times. For example, intra-band switching usuallyhas the same switching time. For another example, inter-band switchingmay also have a same switching time. In case the switching from band Ato band B has a different time for the switching from band A to band C,both times may be reported, or alternatively for simplicity, the maximumof the two times may be reported.

Collision on some symbols, if to occur, is known to UE and eNB before itoccurs.

Collision may cause a UE unable to use some resources (e.g. a subframe),but such resources are still usable by eNB (for other UEs).

Multiple options can be considered; they may be combined.

When a collision may occur, priorities are defined to drop a certaintransmission This consideration is aligned w/ RAN1 agreement; TBD innext meetings.

If SRS switching affects the next subframe:

A/N has higher priority; the SRS switching is dropped.

Aperiodic SRS has higher priority than other UCI/PUSCH.

Periodic SRS has lower priority.

FIG. 45 is a diagram of a carrier based SRS switching scheme. As shown,in this example, if UE SRS switching may collide with the A/N insubframe n+1, the switching in subframe n is dropped.

(E)PDCCH, scheduling request, RI/PTI/CRS may have higher priority thanSRS. A-periodic SRS may have higher priority than other CSI andshort-periodicity P-SRS. If aperiodic SRS collides with (long or short)periodic SRS, the periodic one is dropped. If one periodic SRS collideswith another periodic SRS, the one with shorter periodicity and/or morerecent SRS transmission is dropped.

Alternative, periodic SRS could be assigned with higher priority due toits predictability and hence the network can avoid certain collisionsvia scheduling implementation. For example, periodic SRS with 40 ms orlonger may even be allowed to have higher priority than Ack/Nack.

Furthermore, to avoid collisions and dropping of SRS and othertransmissions, one can define different priorities for differentsubframe sets. For example, on one subframe set, SRS has lower prioritythan other UL transmissions, while on another subframe set, SRS hashigher priority than other UL transmissions. The sets may be related topre-configured UL transmissions (SRS or others) so that thesepre-configured UL transmissions can be better protected. For example, ifthe network wants to protect periodic CSI feedback, it can signal to theUE that the corresponding subframes (and possibly more) are subframeswhere SRS has low priority; SRS may still be configured or triggeredsince the subframe pattern may have a different granularity in time.Similarly this can be used to protect SRS. The network can also scheduleUL transmissions according to the subframe priorities in implementation.

Potential collision can be avoided by scheduling restriction and UEassumption. For example, SRS switching in subframe n may affect the nextsubframe n+1 (especially if the SRS transmission symbol is not earlyenough in subframe n and the switching time is not short enough), butsubframe n+1 may be scheduled for UL transmission (e.g., ACK/NACK for aprevious subframe). If the eNB has information about UE switching timeand hence it can know if a potential collision may occur, it canrestrict its scheduling of UL/DL transmissions (including SRStransmission on a switched-to CC) so that the collision would notactually occur. Correspondingly, the UE should be able to assume that ifa SRS switching is to be performed in subframe n and the SRS switchingaffects subframe n+1, no transmission/reception by the UE is expectedvia network implementation. If SRS switching affects the next subframe:

UE shall assume that no PUCCH (nor PUSCH) be scheduled for the nextsubframe.

eNB should ensure this by no scheduling for the next subframe in DL orUL a few subframes before.

Con: the entire next subframe may not be usable by the UE (still usableby eNB for other UEs).

FIG. 46 is a diagram of a carrier based SRS switching scheme. As shown,in this example, if UE SRS switching causes the beginning symbols ofsubframe n+1 are lost for the UE, then in subframe n-k (associated withn+1), eNB does not schedule the UE in DL (w/ A/N in n+1) or in UL forn+1.

SRS Switching Affects the Next Subframe's A/N:

Suppose SRS trigger is sent in a DCI in subframe n. If there is also aDL grant in subframe n, then both ACK/NACK of the PUSCH and SRS need tobe transmitted in subframe n+k, which may cause a collision. If there isa UL grant in subframe n, then the UL transmission will also occur insubframe n+k, another collision shall occur. New HARQ timing isintroduced, or reuse HARQ timing for interruptions due to measurementgap or SCell activation.

New and flexible SRS transmission timing is introduced, so that SRSswitching is postponed to the next admissible SRS transmissionopportunity without any other scheduled transmission. Alternatively, theSRS may be sent after n+k in the first subframe with SRS switchingconfiguration (e.g., a special subframe), where there is no collision.The SRS switching configuration may be preconfigured with a periodicity(e.g., 5 ms, 10 ms, or 20 ms), and it may include special subframe. AllSRS switching may be restricted to those subframes with SRS switchingconfiguration.

FIG. 47 is a diagram of a carrier based SRS switching scheme. As shown,in this example, if Collision w/ the next subframe A/N may occur w/legacy HARQ timing.

FIG. 48 is a diagram of a carrier based SRS switching scheme. As shown,in this example, if Collision w/ the next subframe A/N is avoided w/ newHARQ timing w/ bundled A/N.

Another Option is Alternative Indication of A/N

If SRS switching affects the next subframe's A/N:

A/N indicated with SRS transmission (e.g., SRS switching is performed ifit is ACK; or via cyclic shifts/sequences of SRS, or via comb, RBallocations etc. For example, if it is Ack, then configuration 1 orparameter set 1 is used for SRS, and otherwise, configuration 1 orparameter set 1 is used for SRS. Multiple Ack/Nack bits may also besupported via combinations of SRS parameter sets. In this case, thenetwork needs to configure the parameter sets and association withAck/Nack. Or the parameter sets for aperiodic SRS may be reused here).

FIG. 49 is a diagram of a carrier based SRS switching scheme. As shown,in this example, if SRS switching collides w/ Nack, SRS switching isdropped; Nack is sent.

FIG. 50 is a diagram of a carrier based SRS switching scheme. As shown,in this example, if SRS switching collides w/ Ack, SRS switching issent; Ack is sent.

Another Option is to: Restrict to Scenarios without Collisions

UE can switch fast enough, e.g., 0 us for intra-band; or

UpPTS is long enough, e.g., with 4 or 6 OFDM symbols for SRS.

Example 1

UE switching time is 0 us→switching in a special or UL subframe causesno collision with the next subframe.

Example 2

UE switching time is 30 us→all SRS symbols in a special subframe (exceptthe last) can be used.

Note that no UCI exists in special subframes, and PUCCH ispunctured/shortened in UL subframes with cell-specific SRS configured.

FIG. 51 is a diagram of a carrier based SRS switching scheme. As shown,in this example, no RF retuning delay is incurred by the UE.

FIG. 52 is a diagram of a carrier based SRS switching scheme. As shown,in this example, a relatively short RF retuning delay is incurred by theUE.

If the switching subframe or next subframe carries PUSCH, PUSCH can bepunctured up to the DMRS of PUSCH. In other words, DMRS should not bepunctured, and if the SRS switching overlaps with DMRS symbols,priority/dropping rules apply. The punctured PUSCH may be transmittedwith higher power, lower MCS levels, or modified beta values so that thereliability can be improved.

Another Option is TA Modification.

Restrict to special subframe SRS switching; network specifies larger TAfor the switched-to CC (if the CCs are in different TAGs).

Via RAR and/or TA Adjustment.

FIG. 53 is a diagram of a carrier based SRS switching scheme. The SRS istransmitted on the last symbol of subframe n on CC2, so the RF retuningfor the switching back operation overlaps with the beginning symbol ofsubframe n+1, if normal TA on CC2 is applied. As shown, in this example,collision w/ subframe n+1 with normal TA for CC2.

FIG. 54 is a diagram of a carrier based SRS switching scheme. The SRS isstill transmitted on the last symbol of subframe n on CC2, but with alarger TA indicated, the UE performs the switching to CC2 and the SRStransmission on CC2 earlier, and hence the UE can switch back to CC1earlier so that it does not overlap with the subframe n+1. As shown, inthis example, No collision w/ subframe n+1 with larger TA for CC2.

An embodiment is to embed an A/N (or UCI) into a PUSCH. One issue withthis is there may be not any PUSCH scheduled for that subframe. Toresolve this, the eNB may indicate the UE that for the upcoming subframewith collision, PUSCH is used instead of PUCCH. The resource allocationof that PUSCH may be sent in DCI. Alternatively, the PUSCH may besemi-persistent scheduled, i.e., configured as SPS. The eNB mayconfigure the SPS periodicity the same as SRS switching periodicity, sothat the subframe affected by SRS switching back operation can usepunctured PUSCH for UCI.

SRS power control should also be introduced to PUSCH-less CCs. Forsupporting closed-loop power control, the network needs to configure anew TPC-SRS-RNTI for a PUSCH-less CC with SRS transmission. The TPCcommand cannot be sent in DL grants and is carried in UL grants in DCI.However, those PUSCH-less CCs have no UL grants for them. Socross-carrier indication of TPC command for PUSCH-less CCs is needed.The cell ID associated with the TPC command needs to be indicated in theUL grant with format 0/4. Alternatively, DL grant can be modified forSRS TPC, with cross-carrier indication or same-carrier indication. GroupDCI 3/3A may be used alternatively, but TPC-SRS-RNTI needs to be used;cross-carrier or same-carrier indication may be allowed. The referencepower Po_PUSCH is not available for the CC without PUSCH, so this needsto be defined. It may be replaced by a new value Po_SRS for thePUSCH-less CC. Alternatively, a different CC's Po (which has PUSCH) maybe used for this PUSCH-less CC. In either case, the network shouldspecify in RRC configuration. The following shows one embodimentconfiguration of SRS and PRACH on a PUSCH-less CC, which is updated fromTS 36.331.

RadioResourceConfigCommon

The IE RadioResourceConfigCommonSIB and IE RadioResourceConfig Commonare used to specify common radio resource configurations in the systeminformation and in the mobility control information, respectively, e.g.,the random access parameters and the static physical layer parameters.Table 3 provides a configuration for a radio resource configurationcommon information element. Tables 4 and 5 provide explanations forvarious SRS parameters.

TABLE 3 RadioResourceConfigCommon information element -- ASN1STARTRadioResourceConfigCommonSIB :: = SEQUENCE { rach-ConfigCommonRACH-ConfigCommon, bcch-Config BCCH-Config, pcch-Config PCCH-Config,prach-Config PRACH-ConfigSIB, pdsch-ConfigCommon PDSCH-ConfigCommon,pusch-ConfigCommon PUSCH-ConfigCommon, pucch-ConfigCommonPUCCH-ConfigCommon, soundingRS-UL-ConfigCommonSoundingRS-UL-ConfigCommon, uplinkPowerControlCommonUplinkPowerControlCommon, ul-CyclicPrefixLength UL-CyclicPrefixLength,..., [[ uplinkPowerControlCommon-v1020 UplinkPowerControlCommon-v1020OPTIONAL -- Need OR ]], [[ rach-ConfigCommon-v1250RACH-ConfigCommon-v1250 OPTIONAL -- Need OR ]], [[pusch-ConfigCommon-v1270 PUSCH-ConfigCommon-v1270 OPTIONAL -- Need OR ]]} RadioResourceConfigCommon :: = SEQUENCE { rach-ConfigCommonRACH-ConfigCommon OPTIONAL, -- Need ON prach-Config PRACH-Config,pdsch-ConfigCommon PDSCH-ConfigCommon OPTIONAL, -- Need ONpusch-ConfigCommon PUSCH-ConfigCommon, phich-Config PHICH-ConfigOPTIONAL, -- Need ON pucch-ConfigCommon PUCCH-ConfigCommon OPTIONAL, --Need ON soundingRS-UL-ConfigCommon SoundingRS-UL-ConfigCommon OPTIONAL,-- Need ON uplinkPowerControlCommon UplinkPowerControlCommon OPTIONAL,-- Need ON antennaInfoCommon AntennaInfoCommon OPTIONAL, -- Need ONp-Max P-Max OPTIONAL, -- Need OP tdd-Config TDD-Config OPTIONAL, -- CondTDD ul-CyclicPrefixLength UL-CyclicPrefixLength, ..., [[uplinkPowerControlCommon-v1020 UplinkPowerControlCommon-v1020 OPTIONAL-- Need ON ]], [[ tdd-Config-v1130 TDD-Config-v1130 OPTIONAL -- CondTDD3 ]], [[ pusch-ConfigCommon-v1270 PUSCH-ConfigCommon-v1270 OPTIONAL-- Need OR ]], [[ uplinkPowerControlCommon-v13xyUplinkPowerControlCommon-v13xy OPTIONAL -- Need ON ]] }RadioResourceConfigCommonPSCell-r12 :: = SEQUENCE { basicFields-r12RadioResourceConfigCommonSCell-r10, pucch-ConfigCommon-r12PUCCH-ConfigCommon, rach-ConfigCommon-r12 RACH-ConfigCommon,uplinkPowerControlCommonPSCell-r12 UplinkPowerControlCommonPSCell-r12,..., [[ uplinkPowerControlCommon-v13xy UplinkPowerControlCommon-v13xyOPTIONAL -- Need ON ]] } RadioResourceConfigCommonSCell-r10 ::= SEQUENCE{ -- DL configuration as well as configuration applicable for DL and ULnonUL-Configuration-r10 SEQUENCE { -- 1: Cell characteristicsdl-Bandwidth-r10 ENUMERATED {n6, n15, n25, n50, n75, n100}, -- 2:Physical configuration, general antennaInfoCommon-r10 AntennaInfoCommon,mbsfn-SubframeConfigList-r10 MBSFN-SubframeConfigList OPTIONAL, -- NeedOR -- 3: Physical configuration, control phich-Config-r10 PHICH-Config,-- 4: Physical configuration, physical channels pdsch-ConfigCommon-r10PDSCH- ConfigCommon, tdd-Config-r10 TDD-Config OPTIONAL -- Cond TDDSCell}, -- UL configuration ul-Configuration-r10 SEQUENCE { ul-FreqInfo-r10SEQUENCE { ul-CarrierFreq-r10 ARFCN-ValueEUTRA OPTIONAL, -- Need OPul-Bandwidth-r10 ENUMERATED {n6, n15, n25, n50, n75, n100} OPTIONAL, --Need OP additionalSpectrumEmissionSCell-r10 AdditionalSpectrumEmission}, p-Max-r10 P-Max OPTIONAL, -- Need OPuplinkPowerControlCommonSCell-r10 UplinkPowerControlCommonSCell-r10, --A special version of IE UplinkPowerControlCommon maybe introduced -- 3:Physical configuration, control soundingRS-UL-ConfigCommon-r10SoundingRS-UL-ConfigCommon, ul-CyclicPrefixLength-r10UL-CyclicPrefixLength, -- 4: Physical configuration, physical channelsprach-ConfigSCell-r10 PRACH-ConfigSCell- r10 OPTIONAL, --CondTDD-OR-NoR11 pusch-ConfigCommon-r10 PUSCH-ConfigCommon } OPTIONAL,-- Need OR ..., [[ ul-CarrierFreq-v1090 ARFCN-ValueEUTRA-v9e0 OPTIONAL-- Need OP ]], [[ rach-ConfigCommonSCell-r11 RACH-ConfigCommonSCell- r11OPTIONAL, -- Cond ULSCell prach-ConfigSCell-r11 PRACH-Config OPTIONAL,-- Cond UL tdd-Config-v1130 TDD-Config-v1130 OPTIONAL, -- Cond TDD2uplinkPowerControlCommonSCell-v1130 UplinkPowerControlCommonSCell- v1130OPTIONAL -- Cond UL ]], [[ pusch-ConfigCornmon-v1270PUSCH-ConfigCommon-v1270 OPTIONAL -- Need OR ]], [[pucch-ConfigCommon-r13 PUCCH-ConfigCommon OPTIONAL, -- Cond ULuplinkPowerControlCommonSCell-v13xx UplinkPowerControlCommonPSCell-r12OPTIONAL -- Cond UL ]] ul-Configuration-r14 SEQUENCE { ul-FreqInfo-r14SEQUENCE { ul-CarrierFreq-r14 ARFCN-ValueEUTRA ul-Bandwidth-r14ENUMERATED {n6, n15, n25, n50, n75, n100} OPTIONAL, -- Need OPadditionalSpectrumEmissionSCell-r10 AdditionalSpectrumEmission }soundingRS-UL-ConfigCommon-r14 SoundingRS-UL-ConfigCommon- r14,prach-ConfigSCell-r14 PRACH-ConfigSCell-r10 OPTIONAL, -- Cond STAG }OPTIONAL, -- Need OP } BCCH-Config ::= SEQUENCE {modificationPeriodCoeff ENUMERATED {n2, n4, n8, n16} } PCCH-Config ::=SEQUENCE { defaultPagingCycle ENUMERATED { rf32, rf64, rf128, rf256}, nBENUMERATED { fourT, twoT, oneT, halfT, quarterT, oneEighthT,oneSixteenthT, oneThirtySecondT} } UL-CyclicPrefixLength ::= ENUMERATED{len1, len2} -- ASN1STOP

TABLE 4 RadioResourceConfigCommon field descriptionsadditionalSpectrumEmissionSCell The UE requirements related toadditionalSpectrumEmissionSCell are defined in TS 36.101 [42]. E-UTRANconfigures the same value in additionalSpectrumEmissionSCell for allSCell(s) of the same band with UL configured. TheadditionalSpectrumEmissionSCell is applicable for all serving cells(including PCell) of the same band with UL configured.defaultPagingCycle Default paging cycle, used to derive ‘T’ in TS 36.304[4]. Value rf32 corresponds to 32 radio frames, rf64 corresponds to 64radio frames and so on. modificationPeriodCoeff Actual modificationperiod, expressed in number of radio frames = modificationPeriodCoeff *defaultPagingCycle. n2 corresponds to value 2, n4 corresponds to value4, n8 corresponds to value 8 and n16 corresponds to value 16. nBParameter: nB is used as one of parameters to derive the Paging Frameand Paging Occasion according to TS 36.304 [4]. Value in multiples of‘T’ as defined in TS 36.304 [4]. A value of fourT corresponds to 4 * T,a value of twoT corresponds to 2 * T and so on. p-Max Pmax to be used inthe target cell. If absent the UE applies the maximum power according tothe UE capability. additionalSpectrumEmissionSCell The UE requirementsrelated to additionalSpectrumEmissionSCell are defined in TS 36.101[42]. E-UTRAN configures the same value inadditionalSpectrumEmissionSCell for all SCell(s) of the same band withUL configured. The additionalSpectrumEmissionSCell is applicable for allserving cells (including PCell) of the same band with UL configured.ul-Bandwidth Parameter: transmission bandwidth configuration, N_(RB), inuplink, see TS 36.101 [42, table 5.6-1]. Value n6 corresponds to 6resource blocks, n15 to 15 resource blocks and so on. If for FDD thisparameter is absent, the uplink bandwidth is equal to the downlinkbandwidth. For TDD this parameter is absent and it is equal to thedownlink bandwidth. ul-CarrierFreq For FDD: If absent, the (default)value determined from the default TX-RX frequency separation defined inTS 36.101 [42, table 5.7.3-1] applies. For TDD: This parameter is absentand it is equal to the downlink frequency. UL-CyclicPrefixLengthParameter: Uplink cyclic prefix length see 36.211 [21, 5.2.1] where len1corresponds to normal cyclic prefix and len2 corresponds to extendedcyclic prefix.

TABLE 5 Conditional presence Explanation TDD The field is optional forTDD, Need ON; it is not present for FDD and the UE shall delete anyexisting value for this field. TDD2 If tdd-Config-r10 is present, thefield is optional, Need OR. Otherwise the field is not present and theUE shall delete any existing value for this field. TDD3 If tdd-Config ispresent, the field is optional, Need OR. Otherwise the field is notpresent and the UE shall delete any existing value for this field.TDD-OR- If prach-ConfigSCell-r11 is absent, the field is optional forTDD, Need NoR11 OR. Otherwise the field is not present and the UE shalldelete any existing value for this field. TDDSCell This field ismandatory present for TDD; it is not present for FDD and the UE shalldelete any existing value for this field. UL If the SCell is part of theSTAG or concerns the PSCell and if ul- Configuration is included, thefield is optional, Need OR. Otherwise the field is not present and theUE shall delete any existing value for this field. ULSCell For thePSCell (IE is included in RadioResourceConfigCommonPSCell) the field isabsent. Otherwise, if the SCell is part of the STAG and if ul-Configuration is included, the field is optional, Need OR. Otherwise thefield is not present and the UE shall delete any existing value for thisfield. STAG This field is mandatory present if the SCell is part of theSTAG; otherwise it is not present and the UE shall delete any existingvalue for this field.SRS Switching-from CC and Switching-to CC

The set of agreements regarding SRS switching between LTE componentcarriers (CCs) reached in RAN1 #86 include:

In addition to all existing parameter configurations

In case the UE supports multiple switching from CCs, selected by

Option 1: rule(s) defined

Option 2: RRC configuration

Details of embodiments for SRS switching-from CC and switching-to CC aredescribed below.

Switching-from CC

For SRS switching, it is necessary to specify the switching-from CC. Theswitching-from CC is the CC whose UL transmission is suspended when SRSis transmitted on the switching-to, PUSCH-less CC. The reason forsuspending the UL transmission on the switching-from CC is to avoidexceeding the UE UL CA capability.

To analyze how to specify the switching-from CC, the following cases areconsidered.

Case 1: The Case of Only 1 Allowed Candidate CC with PUSCH

In this case, for a switching-to, PUSCH-less CC, there is only 1candidate CC with PUSCH as the switching-from CC. Then theswitching-from CC has to be the only candidate CC. The switching-from CCcan be specified in the standards. There is no need for RRCconfiguration of the switching-from CC.

Several scenarios exist in which there is only 1 candidate CC with PUSCHallowed as the switching-from CC for a switching-to CC:

Case 1-1: The UE does not support UL CA.

For this UE, it supports only one CC with PUSCH, namely, the PCell. Theswitching-from CC must be the PCell.

Case 1-2: The UE supports UL CA, but the UE transmitter RF architectureallows only 1 candidate switching-from CC for a switching-to CC.

As an example, suppose a UE supports 2 bands and 2 CCs in each band(CC1/CC2 in band 1 and CC3/CC4 in band 2). CC1 is the PCell which hasPUCCH/PUSCH, and CC3 is the SCell with PUSCH. The UE RF architecture mayuse a dedicated RF for each bands but not the other band. Then aswitching from CC3 to CC2 for SRS transmission on CC2 is infeasible, anda switching from CC1 to CC4 for SRS transmission on CC4 is alsoinfeasible. Therefore, the only switching-from candidate for CC2 is CC1,and the only switching-from candidate for CC4 is CC3. Of course such arestriction has to be reported to the network by the UE so both thenetwork and UE know before the configuration of SRS switching.

This example also shows that, even though it may appear desirable toalways use a SCell with PUSCH as the switching-from CC for a UEsupporting UE CA, this may not be always feasible. A UL-CA-capable UEmay still have to use the PCell as the switching-from CC for somePUSCH-less CCs, despite the fact that it has SCell(s) supporting PUSCH.

Case 2: The Case of Only 1 Preferred Candidate CC with PUSCH

In this case, for a switching-to, PUSCH-less CC, there are multipleallowed candidate CCs with PUSCH to be the switching-from CC, but thereis only 1 preferred candidate CC with PUSCH as the switching-from CC.There are two scenarios:

Case 2-1: The only preferred candidate can be pre-determined.

For this scenario, the only preferred candidate CC can be pre-determinedby the UE capability (which is reported to the network) andconfiguration of CCs (e.g., which CC is the PCell, which CCs supportPUSCH, which CCs need to be the switching-to CCs, etc.). The candidateCC can be either pre-configured via RRC signalling or specified instandards and then determined by UE/eNB without signalling.

There are a few different cases:

Case 2-1-1: The only preferred candidate is determined by RFrequirements in existing standards and efficient requirement.

A UE may support UL CA, and the UE transmitter RF architecture allowsmultiple candidate switching-from CCs for a switching-to CC, but RFrequirements in existing standards limit the candidate switching-fromCCs to be effectively one for a switching-to CC. One example of the RFrequirements in existing standards is the contiguous requirement forintra-band UL CA. As of now, RAN4 RF requirements allow only contiguousUL CA. This limits the switching-from candidates. For example, supposein a band, there are contiguous CC1/CC2/CC3, and CC2 is between CC1 andCC3. Suppose a UE supports all 3 CCs for PDSCH aggregation and CC1/CC2for PUSCH aggregation. If the UE needs to switch to CC3 for SRStransmission, it has to suspend the UL on CC1 to avoid violating thecontiguous requirement. Therefore, though it may appear that either CC1or CC2 can switch to CC3, CC2 is not a preferred candidate andpractically speaking only CC1 can be the switching-from CC. (If CC2 wasselected as the switching-from CC for CC3, then when transmitting SRS onCC3, neither CC1 or CC2 can transmit, an unfavourable design with lowefficiency).

Case 2-1-2: One allowed candidate is the PCell, and the other allowedcandidate is a SCell.

If the PCell is one of the two allowed candidates, it should beprotected as much as possible, and the SCell should be the switching-toCC. (However if the abovementioned contiguous requirements in RFdetermine the PCell is not preferred, then the SCell has to be chosen asthe switching-from CC).

Case 2-1-3: The allowed candidates are SCells, but only one is moredecoupled from the PCell than others do. The coupling may be due to theshared RF by the PCell and a candidate SCell.

It is desirable to select the SCell whose switching-from operation doesnot affect the PCell. For example, if a SCell with PUSCH is in the sameband as the PCell (or share the RF with the PCell), then preferablyanother SCell with PUSCH is selected as the switching-from CC; otherwiseduring the RF retuning due to the SRS switching, the PCell may beinterrupted. This can be done either via a rule or via RRCconfiguration, and the results are the same.

Case 2-1-4: The only one preferred candidate is selected by othercriteria.

If the switching-from operations of all of the candidate SCells affectthe PCell, or if the switching-from operations of none of the candidateSCells affect the PCell, it may be desirable to select a SCell whoseoperations (e.g., UL transmission) are less likely to collide with theSRS switching.

Furthermore, it may be desirable to select a SCell whose operations(e.g., UL transmission) would be consistent with others SRS switchingoperations by the UE.

Furthermore, it may be desirable to select a SCell whose switching fromoperation is the faster than from other candidates.

The above procedure may lead to a unique choice of the switching-fromCC. In this case, the unique choice can be determined by UE/eNB if theyfollow the same selection rules, or alternatively, the eNB decides andconfigures for the UE via RRC signaling, which should have the sameoutcome as the rule-based choice.

Case 2-2: The only preferred candidate can only be determined on thefly.

Case 2-2-1: If the switching-from operations of all of the candidateSCells affect the PCell, or if the switching-from operations of none ofthe candidate SCells affect the PCell, it may be desirable to select aSCell whose operations (e.g., UL transmission) would not collide withthe SRS switching, one example of such is an idle SCell or a deactivatedSCell. That is, this allows the network/UE to utilize the degree offreedom of the carrier domain to avoid collisions. However, this cannotbe pre-configured and has to rely on the eNB and UE to decide on thefly.

Case 2-2-2: Furthermore, it may be desirable to select a SCell whoseoperations (e.g., UL transmission) would be consistent with others SRSswitching operations by the UE.

Case 2-2-3: Furthermore, it may be desirable to select a SCell whoseswitching from operation is the faster than from other candidates.

Case 3: The Case of Multiple Candidate CCs with PUSCH

When the above rules (when applicable) still lead to multipleswitching-from candidates, the following may be considered:

Case 3-1: The switching-from CC may be specified as any one of thecandidate; to avoid ambiguity, RRC configuration of the switching-fromCC can be used. This may have the advantage of network controlling theswitching-from CCs within the cell coverage area.

Case 3-2: The switching-from CC may be specified as the SCell with thehighest CC index.

Case 3-3: The switching-from CC may be any of the candidate SCells. Thechoices of the switching-from CC make no difference to the UEtransmission/reception, and can be transparent to the eNB.

In addition to suspending UL transmission on the switching from CC whenthe switching-to CC is transmitting the SRS, the UL transmission (andpossibly DL reception) on the switching-from CC may be interruptedduring the RF retuning times (before and after the SRS transmission onthe switching-to CC). When a collision occurs due to the interruptions,collision handling can be applied.

In case of dual connectivity, cross-group switching is not supported dueto the lack of fast enough communication/coordination between the MCGand SCG. Therefore, the above discussions were cell-group specific. Whenthe above discussions are applied to the SCG, the PCell refers to thePSCell in the group. Therefore, the switching-from and switching-to CCsare within the same cell group.

The switching-from CC may be deactivated. This does not affect the CC tobe used as a switching-from CC. It may be preferred to select adeactivated SCell as the switching-from CC if rule-based approach isused. Similarly, it may be preferred to select a SCell in DRX as theswitching-from CC if rule-based approach is used.

Observations.

Based on the above elaborated discussions, It is observed herein that:

The switching-from CC for a switching may be pre-determined ordetermined on the fly:

RRC configuration based approach leads to a pre-determined outcome;

If the rules are based on static settings (the UE capability and CCconfigurations) only, the rule-based approach leads to a pre-determinedoutcome;

If the rules depend on dynamic scheduling outcomes, the rule-basedapproach requires the UE/eNB to determine the switching-from CC on thefly.

For most cases, the rule-based approach using only the static settingsand RRC configuration based approach lead to the same outcome, and therules can be easily described and implemented.

For a few cases, the rule-based approach using only the static settingsmay provide some more flexibility than the RRC configuration basedapproach, with somewhat higher complexity at the eNB and UE.

For a few other cases, the rule-based approach based on dynamicscheduling outcomes may provide more flexibility and reduce collision,at the price of increased complexity at the eNB and UE.

For a few cases, switching from any of a set of CCs can be transparentto the network.

Therefore, an embodiment adopts RRC configuration of the switching-fromCC. The RRC configuration of the switching-from CC takes intoconsideration UE capability and RF requirements, and may also take intoconsideration reduced negative impact to other operations.

In an embodiment, the switching-from CC is configured via RRCsignalling.

It is needed for the UE to report sufficient information for SRSswitching configuration, e.g., switching times for inter-band RFretuning and intra-band RF retuning. In some cases, the inter-bandretuning time depends on the specific band pair, then for different bandpairs, the UE needs to report different retuning times. In some cases,the inter-band retuning time depends on the specific CC pair, then fordifferent band pairs, the UE needs to report different retuning times.In some cases, the intra-band retuning time depends on the specific CCpair, then for different CC pairs, the UE needs to report differentretuning times. In some cases, the inter-band and intra-band retuningtime depends on the specific CC pair and the activities of the CC pair,or the band(s) with the CC pair, then for different band pairs, the UEneeds to report the maximum retuning times for the CC pair under allpossible activities. In some cases, the UE may select and report CCpairs to the eNB and the eNB further selects from the reported for SRSswitching.

Switching-to CC and Configuration/Indication

For a SRS switching, the switching-to CC needs to be specified.

For periodic SRS switching, the switching-to CC has to be configured viaRRC signalling.

For aperiodic SRS switching, the switching-to CC may be configured viaRRC signalling, or may be determined via RRC configuration and the A-SRStrigger jointly.

The A-SRS trigger contains a 3-bit CIF. Then the switching-to CC is theCC associated with the CIF. This may be used for A-SRS trigger based onDL DCI and group DCI, and the CIF has to be enabled and configured,i.e., cross-carrier scheduling/indication is configured.

The A-SRS trigger does not contain CIF, but the bit(s) sent in the A-SRStrigger is associated with a CC via RRC configuration. Then theassociated CC is the switching-to CC. For example, for a CC that the UEis monitoring the A-SRS trigger, the parameter set 1 is configured forSRS transmission on CC1, the parameter set 2 is configured for SRStransmission on CC2, and the parameter set 3 is configured for SRStransmission on CC3, and so on. Note that multiple parameter sets can beconfigured for the SRS transmission on a same CC (the SRS transmissionconfigurations may differ for these different parameter sets). This maybe used for A-SRS trigger based on DL DCI and group DCI, and it does notrequire cross-carrier scheduling be configured.

The A-SRS trigger does not contain CIF, and no bit(s) sent in the A-SRStrigger is associated with a CC via RRC configuration. Then the CCreceiving the A-SRS trigger is the switching-to CC. This may be used forA-SRS trigger based on DL DCI and group DCI, and it does not requirecross-carrier scheduling be configured.

The above three options can be combined and all supported. If the UE isconfigured with cross-carrier scheduling for some carriers, it isreasonable to reuse the CIF for SRS switching for these carriers;otherwise, the A-SRS trigger parameter sets or same-carrier indicationcan be used for specifying the switching-to CC.

In an embodiment, the switching-to CC of a P-SRS is specified by RRCconfiguration signalling.

In an embodiment, the switching-to CC of a A-SRS is specified by CIF (ifconfigured), A-SRS trigger bit and associated parameter set configuredby RRC, RRC configuration signalling alone, or the CC receiving theA-SRS trigger.

Switching for RACH on a PUSCH-Less CC

For RACH on a PUSCH-less CC, the switching-from CC and switching-to CCalso need to be specified. The switching-to CC is the CC indicated bythe PDCCH order for the RACH (i.e., if CIF is present, then the CCassociated with the CIF value is the one to transmit RACH; otherwise theCC receiving the PDCCH order is the one to transmit RACH), which is thesame behavior as the current RACH. For the switching-from CC, there area few alternatives:

The switching-from CC for the PDCCH order of the RACH is pre-configuredby RRC signalling. In this case, for the same CC, the associatedswitching-from CC for RACH and switching-from CC for SRS could bedifferent.

The switching-from CC for the RACH on a CC is specified to the same asthe switching-from CC for the SRS switching. This is a simple solution,but it cannot be used for a CC whose switching-from CC is notpre-determined. If the option of SRS switching-from CC determined on thefly is not supported, this option should be supported for itssimplicity. Alternatively, the rules used for determining theswitching-from CC for SRS switching can be applied here for theswitching for RACH, e.g., avoid/reduce interruption to the PCell orPSCell, utilize the deactivated CC or CC in DRX, etc.

In an embodiment, the switching-to CC for RACH on a PUSCH-less CC is theCC indicated by the PDCCH order.

In an embodiment, the switching-from CC for RACH on a PUSCH-less CC isthe same as the switching-from CC for the associated SRS switching.

DCI Design for SRS Switching

The set of agreements regarding SRS switching between LTE CCs reached inRAN1 #86 include:

-   Down selection from TPC command options:    -   Option 1: by UL grant DCI 0/4 (with cross-carrier indication)    -   Option 2: by DL DCI (with cross-carrier indication)    -   Option 3: by group DCI    -   Adopt Option 3 and only apply to SRS-only CC without PUSCH        -   Joint group DCI for triggering and TPC        -   FFS: Number of bits for each UE and the meaning for the            states of the field        -   Introduce RNTI for the group-   For A-SRS, trigger is carried in:    -   DL scheduling DCI and group DCI    -   Group DCI is only used for SRS-only CC without PUSCH

Details of embodiments for downlink control information (DCI) design aredescribed below.

Group DCI Jointly for TPC Command and A-SRS Trigger

A new group DCI format is needed to support joint indication of TPCcommand and A-SRS. The existing group DCI format 3/3A for TPC commandscan be considered as a baseline for the new design while incorporatingA-SRS triggers. Several aspects are discussed below.

Search Space for the DCI

The group DCI needs to be transmitted in a search space common to agroup of UEs instead of in UE-specific search spaces. One option is touse the common search space in the PCell, but this then requiressignificant signalling overhead for cross-carrier indication and maycause more collisions in the common search space. Another option is touse a search space in each CC without PUSCH with the lowest indexed CCEs(0˜3 for aggregation level 4 and 0˜7 for aggregation level 8), similarto the case of UE monitoring DCI format IC on each LAA SCell introducedin Rel-13. If more search space is needed (e.g., to support two DCIs totwo groups of UEs in one subframe), CCEs 4˜7 may be included foraggregation level 4. Yet another option is to use a search space in eachCC that the UE monitors PDCCH with the lowest indexed CCEs. Note thatthe PDCCH on these CCs may contain CIF for cross-carrier scheduling onanother CC, and the same cross-carrier indication relation can beutilized for indicating the CC for TPC command and A-SRS trigger.

It is observed herein that the UE needs to monitor the search space withthe lowest CCE indexes associated with each SRS-switching CC, on thePCell and a set of SCells, or all the serving cells or all the servingcells on which the UE monitors PDCCH.

Payload Size for the DCI

To help reduce the number of blind detections by a UE, the payload sizeof the group DCI (including possible zero-padding) is preferred to beequal to the size of a DCI that the UE already monitors. Generally, theUE monitors DCI format 0/1A associated with every CC, so it is desirablethat the payload size of the group DCI is equal to that of DCI format0/1A on the same CC. Note that DCI formats 3/3A also have the same sizeas DCI formats 0/1A.

It is observed herein that the group DCI payload size (with padding)should be the same as DCI format 0A.

RNTI for the DCI

AN RNTI common to the group of UEs in a carrier is needed. Each UE inthe group will be configured with the group RNTI. The range of the RNTIvalues can be the same as those for TPC of PUSCH/PUCCH. In case thenumber of UEs in a carrier is large, there may be a need to configuremore than one group RNTI on the carrier so that different groups of UEsare associated with different group RNTIs. One RNTI may be configuredfor all SRS-switching CCs of a UE, or alternatively, each SRS-switchingCC is configured with a CC-specific RNTI. If the new DCI format supportsTPC-only content and TPC+trigger content, they may also bedifferentiated by different group RNTIs.

It is observed herein that a group RNTI needs to be configured for thegroup DCI.

Indication of UEs and CCs in the DCI

One option for the DCI design is that the DCI indicates only the UE butnot the switching-to CC of the UE. This corresponds to the case of nocross-carrier indication. In this case, the UE needs to monitor thegroup DCI on each CC with SRS switching, but the CIF needs not bepresent in the DCI and the overall overhead may be reduced. Theindication of the UE can be similar to that in DCI format 3/3A, i.e.,each UE associated with the group is configured with an index of alocation within the PDCCH.

Another option is to indicate both the UE and the CC associated with theTPC command and A-SRS triggering. In other words, cross-carrierindication is utilized. Note that cross-carrier indication from only thePCell is not desirable as it may need up to 5 bits (or equivalent) tospecify the CC for a UE. However, the current cross-carrier indicationmechanism of up to 3-bit CIF may be adopted. In addition, similar to DCIformat 3/3A, each UE associated with the group is also configured withan index of a location within the PDCCH.

It is observed herein that the group DCI indicates a UE via an index ofa location in the PDCCH, and indicates a CC of the UE via 0-bit CIF(same-carrier indication) or 3-bit CIF (cross-carrier indication).

TPC Commands in the DCI

All DCI formats with TPC commands use a 2-bit field for the TPC commandfor PUSCH/PUCCH, except that in 3A, only 1 bit is used. Therefore, it isreasonable to support a 2-bit field in the new group DCI for SRS TPCcommand, and if a compact form is needed, a 1-bit field may also beconsidered.

It is observed herein that the group DCI supports a 2-bit field or a1-bit field for each TPC command.

A-SRS Triggers in the DCI

In DCI formats 0/1A/2B/2C/2D/6-0A/6-1A, a 1-bit trigger is used forA-SRS, whereas in DCI format 4, a 2-bit trigger is used. For the newgroup DCI, both may be supported. For the case of a 1-bit trigger, oneA-SRS parameter set can be supported, while for the case of a 2-bittrigger, three A-SRS parameter sets can be supported. If more A-SRSparameter sets are needed, at most one more bit (i.e., at most a 3-bittrigger) may be considered. On the other hand, if for each DL CC(include each FDD CC if aggregated), there can be up to 3 parameter setsconfigured, this could lead to in total a sufficiently large number ofparameter sets usable for aperiodic SRS. In other words, RAN1 mayconsider either increasing the number of SRS request bits or supportingcarrier-specific SRS parameter set configuration.

It is observed herein that the group DCI supports at least the 1-bit and2-bit trigger for A-SRS.

The time offset between the trigger and the associated SRS transmissionhas already been defined in existing standards and can be reused for SRSswitching. However, if there is a need to modify the time offset for SRSswitching to help avoid collision with other transmissions, a timeoffset may be included with the trigger, similar to eLAA SRS trigger.The time offset in the group DCI may be common to all SRS requests inthe DCI.

For the group DCI for TPC command and A-SRS, an embodiment providessupport for one or more of the following:

A search space with the lowest indexed CCEs on all the serving cells(same-carrier indication) or all the serving cells on which the UEmonitors PDCCH (cross-carrier indication)

-   -   Same payload size as DCI formats 0/1A (with padding)    -   Group RNTI    -   0-bit CIF (same-carrier indication) or 3-bit CIF (cross-carrier        indication)    -   2-bit TPC command and 1-bit TPC command in compact format    -   At least 1-bit and 2-bit trigger    -   Optionally a time offset indication.

The above discussion may lead to a large number of combinations for theDCI format contents. To simplify, down selection of the DCI formatcontents should be considered.

First, there are cases that A-SRS may not be configured or triggered,but TPC command is needed for P-SRS. Therefore, it makes sense to have aDCI format with TPC only. This is effectively the DCI formats 3/3A, buton a CC supporting P-SRS transmission or SRS transmission. No otherfield needs to be included in the DCI format. The RNTI may be called asSRS-TPC-RNTI. Note that the length of DCI formats 3/3A is the same asDCI formats 0/1A.

Second, when A-SRS is configured, the group DCI needs to contain SRSrequests for A-SRS and their associated TPC commands. There are at leastthese combinations: 1) 0 or 3 bit CIF, 2) 1 or 2 bit TPC, and 3) 1 or 2bit trigger. To further simplify, note that the UE already needs tomonitor the TPC-only DCI format on each CC with SRS, so it is reasonablethat the UE monitors every CC with A-SRS for the TPC+trigger DCI formatwithout considering cross-carrier indication. Then, 1 or 2 bit TPC and 1or 2 bit trigger may be supported, which amounts to 4 combinations andmay be differentiated by a 2-bit flag in the DCI or RNTI. Alternatively,further down selection can be considered.

An embodiment for the group DCI, focus on the following down selections:

TPC-only DCI (similar to 3/3A) on every CC with P-SRS, and TPC+triggerDCI on every CC with A-SRS, with 1 or 2 bit TPC and 1 or 2 bit trigger.

TPC-only DCI

-   -   a. Reuse DCI formats 3/3A    -   b. UE monitors this format on every CC with P-SRS in a search        space with the lowest indexed CCEs    -   c. With a configured group RNTI

TPC+trigger DCI

-   -   a. With 1 or 2 bit TPC and 1 or 2 bit trigger    -   b. Same payload size as DCI formats 0/1A (with padding)    -   c. UE monitors this format on every CC with A-SRS in a search        space with the lowest indexed CCEs    -   d. With a configured group RNTI    -   e. Possibly with a time offset indication.

Other variations can be considered. E.g., a one bit flag is included inthe DCI to tell the UE if the DCI is for TPC only or not, or a one bitflag is included in the DCI to tell the UE if the DCI is for triggeronly or not, or a two bit flag is included in the DCI to tell the UE ifthe DCI is for TPC only, TPC+trigger, trigger only. In addition, flagscan be used to tell the UE the lengths or presence of some fields, e.g.,1 or 2 bit TPC, 1 or 2 bit trigger, presence of timing offset, presenceof CIF, etc. The flags may be jointly encoded. Alternatively, the flagsmay not be present, and the DCI format contents differences aresignalled via group RNTIs. In other words, for UEs using differentformats, they are configured in different groups and each group isassociated with a dedicated RNTI.

DL DCI for A-SRS Trigger

Currently, aperiodic SRS is configured via RRC signalling and triggereddynamically via DCI formats 0/1A/2B/2C/2D/4 for TDD and 0/1A/4 for FDD.Among them, DCI formats 1A/2B/2C/2D are for DL. These DCI formats may beenhanced to support A-SRS switching. There seems to be no need tosupport other DL DCI formats for A-SRS switching. If aperiodic SRS isnot configured on a serving cell, the SRS request field may stillpresent and the current standards do not define how the UE may utilizeit. This field is now useful to trigger A-SRS on the associated CC. Theassociated CC may be the CC receiving the DCI (if CIF is not configured)or a different CC (if CIF is configured). No change in the standards isneeded to support this behavior except that RRC signalling needs toconfigure A-SRS on the associated CC.

Similar to the “A-SRS triggers in the DCI” section above, the number ofbits and time offset are as follows. The DL DCI formats have a 1-bittrigger. It is likely needed to increase the trigger to be at least 2bits. This changes the DCI payload sizes and the network shouldconfigure the UEs if the new payload size is used. In addition, the timeoffset may be included so that the triggered SRS switching andtransmission can be at a different time from the ACK/NACK associatedwith the DL DCI.

For DL DCI 1A/2B/2C/2D for A-SRS, an embodiment provides support for a2-bit trigger and optionally a time offset indication.

Other Considerations on SRS Switching

The set of agreements regarding SRS switching between LTE CCs reached inRAN1 #86 include:

-   -   R14 SRS switching supports RF retuning time no longer than X us    -   Option 1: X=200    -   Option 2: X=300    -   Option 3: X=500    -   Option 4: X=900

In addition, in RAN4 discussions, whether to support SRS switching to adeactivated CC was brought up. Details of embodiments for maximumswitching time support for Rel-14 and SRS switching to a deactivated CCare described below.

Maximum RF Switching Time to be Supported in Rel-14 SRS Switching

The following RF switching times have been agreed by RAN4:

[RAN4]: Given that the RF switching time may have some dependency on theCA scenarios and UE implementation, RAN4 agrees that the RF switchingtime can be defined in the following values:

-   -   0 us    -   30 us    -   100 us    -   200 us    -   300 us    -   500 us    -   900 us

For RAN1 design, it would be useful to decide on a maximum value of theswitching times so that RAN1 can provide efficient support for UEs withswitching times no longer than the maximum value. To select the maximumvalue, it is desirable to consider the switching times that can have noor little negative impact on other transmissions and receptions. If aswitching time always leads to negative impact on other transmissionsand receptions for any configurations, then RAN1 can consider how toefficiently support such a switching time in later releases.

It can be seen that for a switching time of 500 us or longer, there isalways a negative impact on other transmissions and receptions for anyconfiguration. To see this, notice that 500 us amount to 8 OFDM symbols.Regardless where the SRS is transmitted in currently supported SRSsymbol positions, the next subframe is affected. Therefore, in anembodiment X should be strictly smaller than 500 us.

On the other hand, if the switching time is 300 us or shorter, thereexists at least one configuration that no other transmissions orreceptions are affected at all, even if the maximum timing advancedifference (32.47 us) is considered. To see this, notice that 300 usplus 32.47 us amount to at most 5 OFDM symbols. With TDD specialsubframe configuration 0 (3 OFDM symbols for DwPTS) and 6 OFDM symbolsfor UpPTS, SRS transmission can be performed at the first symbol of theUpPTS, and neither the DwPTS of the current subframe or any symbol ofthe next subframe is affected by the SRS switching. If the switchingtime is shorter, more configurations can support SRS switching and moreSRS transmission positions can be allowed without affecting otheroperations. Therefore, in an embodiment X is chosen as 300 us.

In an embodiment, R14 SRS switching supports RF retuning time no longerthan 300 us.

Deactivated Carriers

It should be noted that for a deactivated carrier, SRS is nottransmitted according to current standards. SRS switching between LTEcomponent carriers should also follow the same principle, i.e., a UEwill not switch to a PUSCH-less TDD carrier for SRS transmission if thatcarrier is deactivated. This also helps to reduce SRS switchingoverhead. A LS from RAN1 to RAN4/2 can be considered to clarify thisissue.

The following excerpt from TS 36.321 is included for information:

5.13 Activation/Deactivation of SCells

The MAC entity shall for each TTI and for each configured SCell:

-   -   if the SCell is deactivated:    -   not transmit SRS on the SCell;”

In an embodiment, for SRS switching, there is no switching to adeactivated CC.

Power Headroom Report for SRS Switching

Introduction

The set of agreements regarding SRS switching between LTE CCs regardingthe power headroom report for the power control mechanism reached inRAN1 #86 include:

-   Support 2 types of PHR as in Rel-13    -   Details FFS

Details of embodiments for the two types of power headroom reports forSRS on TDD CCs without PUSCH are described below.

Consideration for PH for SRS on TDD CCs without PUSCH

The power control formula for SRS on TDD CCs without PUSCH is, if the UEtransmits the SRS in subframe i for serving cell c, the transmit powercan be calculated based on the formula below:P _(SRS,c)=min[P _(CMAX,c)(i),{10 log₁₀(M _(SRS,c))+P_(O_SRS,c)(j)+α_(SRS,c)(j)·PL _(c) +f _(SRS,c)(i)}] [dB]where P_(CMAX,c)(i) is the configured UE transmit power defined inTS36.101 in subframe i for serving cell c; P_(O_SRS,c)(j) andα_(SRS,c)(j) are parameters defined for SRS power control in subframe ifor serving cell c, where j=0 for P-SRS and j=1 for A-SRS; M_(SRS,c) isthe bandwidth of the SRS transmission in subframe i for serving cell cexpressed in number of resource blocks; and f_(SRS,c)(i) is the currentSRS power control adjustment state for serving cell c.

A remaining issue is the PHR for SRS on TDD CCs without PUSCH. Based onthe power control formula, if the UE transmits the SRS in subframe i forserving cell c, the PH can be calculated based on the formula below:PH _(SRS,c)(i)=P _(CMAX,c)(i)−{10 log₁₀(M _(SRS,c))+P_(O_SRS,c)(j)+α_(SRS,c)(j)·PL _(c) +f _(SRS,c)(i)} [dB]where P_(CMAX,c)(i) is the configured UE transmit power defined inTS36.101 in subframe i for serving cell c; P_(O_SRS,c)(j) andα_(SRS,c)(j) are parameters defined for SRS power control in subframe ifor serving cell c, where j=0 for P-SRS and j=1 for A-SRS; M_(SRS,c) isthe bandwidth of the SRS transmission in subframe i for serving cell cexpressed in number of resource blocks; and f_(SRS,c)(i) is the currentSRS power control adjustment state for serving cell c.

If the UE does not transmit SRS in subframe i for serving cell c, the PHcan be calculated based on the formula below:PH _(SRS,c)(i)={tilde over (P)} _(CMAX,c)(i)−{P_(O_SRS,c)(1)+α_(SRS,c)(1)·PL _(c) +f _(SRS,c)(i)} [dB]where {tilde over (P)}_(CMAX,c)(i) is computed assuming MPR=0 dB,A-MPR=0 dB, P-MPR=0 dB and ΔT_(C)=0 dB, where MPR, A-MPR, P-MPR andΔT_(C) are defined in TS36.101.

In an embodiment, the two types of PH_(SRS,c)(i) are calculated based onagreed SRS power control formula, and there are various alternatives onhow the SRS-only PHR is triggered and reported.

Collision Handling for SRS Switching

Analysis of Collisions

There are collisions caused by different reasons and they may takedifferent forms. To effectively handle collisions, the followinganalysis of collisions is provided.

Type 1: A Collision Caused by UE Capability Limitations or RequirementViolations

If the operations configured/scheduled for a UE exceed the UEcapability, a collision may occur. In addition, if the operationsconfigured/scheduled for a UE violate requirements/regulations, such asband combination requirements, a collision may occur.

For example, for a UE capable of transmitting in UL on one CC at a time,to transmit SRS on a switching-to CC while at the same time transmittingon the switching-from CC would exceed the UE UL capability and hencethis is a collision. In this case, only one transmission can be allowedat a time. See [1] for discussions on switching-to and switching-from CCfor SRS switching.

For another example, for a UE supporting 2 UL CC CA, transmitting SRS onCC1 in Band A and another signal on CC2 in Band B may be a collision, ifthe UE can support only one band at a time, or if a RF requirementforbids simultaneous transmissions on Bands A and B.

For yet another example, configuring/scheduling a UE to perform twotransmissions on overlapping resources also leads to a collision, suchas indicating the UE to transmit A-SRS on the same symbol as aconfigured P-SRS causes a collision.

Type 2: A Collision Caused by RF Retuning

Collisions may occur during RF retuning.

For example, during the switching from CC1 to CC2, RF retuning may causeall CCs within the same band as CC1 not able to transmit, and it mayalso cause all CCs within the same band as CC2 not able to transmit.

For another example, if the SRS transmission on a PUSCH-less CC isperformed in the last OFDM symbol of a subframe, and if the UE RFretuning time is non-zero, then the next subframe (UL or DL) will beaffected.

Type 1 collisions may occur on the symbols for SRS transmission by theswitching-to CC. On the other hand, Type 2 collisions may occur duringthe RF retuning time of a SRS switching, but not on the symbols for SRStransmission by the switching-to CC. Both UL and DL may be affectedduring the collision. Likewise, RACH transmission on a PUSCH-less CC mayalso cause both types of collisions. Collision handling mechanismsshould be applied to all the signals on all OFDM symbols of all affectedCCs during the collision.

Collision handling mechanisms should be applied to all the signals onall OFDM symbols of all affected CCs during the collision.

Collision Handling for SRS on TDD CCs without PUSCH

In case of collisions, how to determine which transmission (orreception) should be kept/dropped and enhancements to avoid collisionsshould be defined.

The potential solutions could be:

Option 1: Define priority/dropping rules.

Option 2: Allow punctured signals.

Option 3: Change A-SRS timing or HARQ timing.

In Option 1, given a certain configured SRS transmission, when it is incollision with PUSCH/PUCCH/PRACH/etc. in another UL carrier, the factorsincluding periodic/aperiodic SRS type and channel/UCI type as well asPCell/SCell type, could be considered when deciding the dropping ruleand prioritized transmission.

SRS switching can have higher priority than normal data transmissions(PUSCH/PDSCH).

DL control channels, (E)PDCCH should have higher priority than SRSswitching. Signals carrying RRC configuration information, MAC controlinformation, and associated feedback should have higher priority thanSRS switching.

As a general guideline, signals carrying ACK/NACK, SR, and signalsinvolved in RACH procedure, should have higher priority than SRSswitching. However, if the negative impact of SRS switching on ACK/NACKcan be limited (e.g., via RAN4 requirement of lost ACK/NACK for a CC tobe no more than 0.5% due to SRS switching), A-SRS and long-periodicityP-SRS may have higher priority than ACK/NACK.

SRS switching should have higher priority than CSI feedback on TDD CCsas SRS provides a better means of obtaining CSI. However, long-term CSIfeedback carrying RI/PTI/CRI for FDD CCs should have higher prioritythan SRS switching.

The priority/dropping rules should be applied after collision avoidancevia puncturing signals is applied. In other words, if puncturing signalscan resolve the collision, then the priority/dropping rules are notapplicable; otherwise, the priority/dropping rules are applied.

Embodiment

Consider the following priority/dropping rules:

(E)PDCCH, RI/PTI/CRI for FDD, RRC/MAC signaling, SR, RACH,[ACK/NACK]>A-SRS>long-periodicity SRS>[other ACK/NACK]>short-periodicitySRS>other CSI>normal PUSCH/PDSCH.

In option 2, one can introduce some forms of punctured PUCCH/PUSCH/PDSCHformats to handle a collision of SRS transmission on a differentcarrier. PUCCH/PUSCH/PDSCH symbols overlapping with SRS switching may bepunctured so that punctured signals and the SRS switching could both bemaintained.

This could consider to reuse existing partial PDSCH/PUSCH as in LAA/eLAAas much as possible, such as partial ending subframe, subframe with onlyone slot, PUSCH without the 1^(st) or the last symbol, etc. The numberof symbols to be transmitted/received needs not be indicated to the UEsince both eNB and UE know how many symbols are in overlap with SRSswitching.

Punctured PDSCH can be considered.

Punctured PUSCH can be considered. However, no DMRS symbol of the PUSCHshould be punctured; if DMRS would be impacted, priority/dropping rulesshould be applied. In addition, if ACK/NACK is embedded in the PUSCH, noACK/NACK symbol should be punctured; if ACK/NACK would be impacted,priority/dropping rules should be applied.

Punctured PUCCH can be considered. However, no DMRS symbol of the PUCCHshould be punctured; if DMRS would be impacted, priority/dropping rulesshould be applied. The puncturing may or may not lead tonon-orthogonality among multiplexed UEs depending on the PUCCH formatand means of multiplexing. If a PUCCH format defined in TS36.213 usesorthogonal cover code in time-domain on data symbols (not DMRS symbols)of PUCCH, then puncturing leads to non-orthogonal multiplexing andshould not be used; otherwise, PUCCH data symbols can be punctured andorthogonality is preserved.

Embodiment

Partial PDSCH/PUSCH subframes, punctured PDSCH, PUSCH (not impactingDMRS symbol or ACK/NACK symbol), and PUCCH (not impacting DMRS) formatscan be considered.

In option 3, change HARQ timing or A-SRS transmission timing could beconsidered. Suppose SRS trigger is sent in a DCI in subframe n. If thereis also a DL grant in subframe n, then both ACK/NACK of the PUSCH andSRS need to be transmitted in subframe n+k, which may cause a collision.Hence, it could be considered to change ACK/NACK timing to be in a latersubframe by reusing the ACK/NACK timing in eIMTA. Alternatively, the SRSmay be sent after n+k in the first subframe with SRS switching allowed(e.g., a special subframe), where there is no collision. The SRS triggermay also be associated with a timing offset, similar to eLAA SRStrigger, which indicates to the UE a different opportunity for SRSswitching. eLAA has 3 bits to indicate the offset to subframe n+k interms of number of subframes, i.e., 000 is for 0 subframe offset, and soon. For SRS switching, few bits can be considered, such as one or twobits. Also for SRS switching, the offset is in terms of the SRStransmission opportunity as configured to the UE, which corresponds toT_(SRS,1), T_(offset,1), and k_(SRS) in T536.213.

Yet another embodiment for collision handling is to enable PUCCH/PUSCHtransmission on switching-to CC. If the UE switches to a CC for SRS,then the UE stays on the CC for other UL Tx until the next switchingoccurs. The pro is that no dropping of transmissions. This effectivelyleads to UL fast carrier switching.

Multiple Antenna Support for SRS

For TDD system, sounding is very important for system performanceimprovement. The DL CSI is greatly dependent on sounding. Since all ofthe antennas would be utilized in DL reception, it is needed to supportsounding for all of the antennas of UE.

With the different DL and UL capabilities, UE can sound one or severalantennas at a time. The following summaries the different UL capabilitycases:

-   1. 2 Rx in DL    -   a. 1 Tx in UL, not supporting transmit antenna selection    -   b. 2 Tx in UL    -   c. 1 Tx in UL, supporting transmit antenna selection-   2. 4 Rx in DL    -   a. 1 Tx in UL, not supporting transmit antenna selection    -   b. 2 Tx in UL, not supporting transmit antenna selection    -   c. 4 Tx in UL    -   d. 1 Tx in UL, supporting transmit antenna selection    -   e. 2 Tx in UL, supporting transmit antenna selection

For Cases 1a, 2a, 2b, it is impossible to sound all the antenna sincetransmit antenna selection is not supported, that is, UE is not capableof transmitting on the other antenna(s). These cases are excluded in ourconsiderations below.

For 2 antenna cases, UE can support sounding of the 2 antennas throughUL 2×2 MIMO (Case 1b) or 2 antenna switching (Case 1c), which arealready supported in specification for different capability UE. With theintroduction of SRS carrier based switching, sounding of the 2 antennascan be performed on a PUSCH-less carrier without additional standardimpact, via RRC configuration for P-SRS and RRC configuration plus DCIindication for A-SRS.

For Case 2c, the sounding by all 4 Tx antennas is already supported inR13, and it can be combined with SRS carrier based switching withoutadditional standard impact. However, UEs supporting 4 Tx in UL rarelyexist in the real network. It may need a long time before the UE withuplink 4 Tx capability can be popularized. For 4 Rx in DL, the typicalUE capabilities should be Cases 2d and 2e. Therefore, to sounding allthe 4 uplink antenna, Cases 2d and 2e should be the main focus for SRSenhancement.

For 4 antenna cases, if UE has only 1 UL Tx antenna capability (Case 2d)or 2 UL Tx antenna capability (Case 2e), 4 antenna switching should beintroduced to sound all the antennas. The 4 antenna switching willbenefit the sounding of all the CCs, including CCs with or withoutPUSCH.

The sounding enhancement on frequency and spatial domains willsignificantly improve the DL throughput, which is the motivation of SRScarrier based switching WI. It is proposed to introduce 4 antennasswitching (Cases 2d and 2e) for the SRS with carrier switching.

In Rel-13, for 2 antenna switching, the Tx antenna is switched at eachSRS transmission instance for P-SRS. 2 Tx antenna switching over onecarrier is performed based on a predefined pattern calculated from RRCconfigured parameters. For a UE with 4 antennas, the antenna switchingshould include all the 4 antennas. With the carrier switching in Rel-14,UE can also perform antenna switching for SRS transmission combined withcarrier based switching. Therefore, the sounding can be preformed bydifferent carriers and antennas.

The switching of antennas for SRS transmission with carrier switchingcan be based on a predefined pattern calculated from RRC configuredparameters. The mechanism is similar with 2 Tx antenna switchingsupported in Rel-13. The predefined switching pattern should facilitatethe sounding of all antennas. All the antennas should have theopportunity of SRS transmission on CCs with or without PUSCH. Theenabling of antenna switching with carrier switching can be configuredby RRC. The carrier switching for SRS transmission will perform theantenna switching based on the predefined pattern.

For SRS carrier based switching, P-SRS and A-SRS are both supported. ForCCs with or without PUSCH, SRS should be configured separately by RRC.For CCs with PUSCH, legacy sounding procedure can be reused for all thecases except 2d, 2e. For cases 2d and 2e, new antenna switching formulacan be defined to support sounding of all the 4 Tx antennas. For case2e, the 4 Tx antennas can be divided into 2 groups with 2 antennas ineach group. Antenna switching can be performed both between antennagroups and between antennas within a group.

For CCs without PUSCH, new sounding procedure can be defined to addressthe combination of antenna and carrier switching. The UE capable of UL4×4 MIMO can sound 4 antennas at a time. For the UE with 1 UL Tx antennacapability, 4 Tx antenna switching is used for sounding 1 antenna at atime. With RF retuning time, the frequent carrier switching will bringlarger retuning time overhead. To support 4 Tx antenna switching, theoverhead of switching antennas+carriers should be improved.

The latency of sounding all the antennas and carriers may be large. Toreduce the latency of sounding, it is better to sound all the 4 Txantennas on a CC when carrier switching proceeds for SRS on the CC. TheSRS from 4 Tx antenna should be transmitted on different symbols withshort interval to reduce latency. For TDD system, at least forPUSCH-less CCs, multiple symbols (e.g., all 4 additional symbols inUpPTS) in a subframe can be used for SRS transmission of 4 Tx antennasby the same UE. In current TS36.213, it has “For TDD serving cell, andif the UE is configured with two or four additional SC-FDMA symbols inUpPTS of the given serving cell, all can be used for SRS transmissionand for trigger type 0 SRS at most two SC-FDMA symbols out of theconfigured additional SC-FDMA symbols in UpPTS can be assigned to thesame UE.” If such a restriction is removed, then all 4 additionalsymbols in UpPTS can be used by the same UE for SRS transmission. Inaddition, for trigger type 0, if SoundingRS-UL-ConfigDedicatedUpPTsExtis configured and SoundingRS-UL-ConfigDedicated are configured, bothshall be used. For trigger type 1, ifSoundingRS-UL-ConfigDedicatedAperiodicUpPTsExt andSoundingRS-UL-ConfigDedicated are configured, both shall be used.

For SRS switching requirements, there are a few options:

1) No requirement on maximum interruption.

2) Max interruption=1 subframe. This implies that SRS switching cannotaffect the next subframe, then A/N won't be affected, and the networkcarefully configures suitable UEs for SRS switching. If the interruptionis limited to 1 subframe, for cases with aligned TDD UL/DLconfiguration, the interruption is only in the special subframe or thelast symbol of UL subframe. The special subframe does not carry A/N. TheSRS on the last symbol of UL subframe does not affect A/N. For FDD+TDDwithout timing alignment between TDD and FDD, this may lead to noswitching from FDD CC to TDD CC if the switching leads to 2 lost ULsubframes in FDD.

3) Max interruption=2 subframes.

In addition (or alternatively), if a requirement “A/N loss rate is nolarger than 0.5%” is introduced, then the standards do not have toimpose other hard restrictions but leave the network to decideconfigurations so that the A/N loss rate requirement is met; other thanthat the network is totally free to decide how the SRS switching isperformed. Though not really solving the interruption problem orcollision problem, it limits the negative impacts of interruption andcollision.

FIG. 55 illustrates a block diagram of an embodiment processing system5500 for performing methods described herein, which may be installed ina host device. As shown, the processing system 5500 includes a processor5504, a memory 5506, and interfaces 5510-5514, which may (or may not) bearranged as shown in FIG. 55. The processor 5504 may be any component orcollection of components adapted to perform computations and/or otherprocessing related tasks, and the memory 5506 may be any component orcollection of components adapted to store programming and/orinstructions for execution by the processor 5504. In an embodiment, thememory 5506 includes a non-transitory computer readable medium. Theinterfaces 5510, 5512, 5514 may be any component or collection ofcomponents that allow the processing system 5500 to communicate withother devices/components and/or a user. For example, one or more of theinterfaces 5510, 5512, 5514 may be adapted to communicate data, control,or management messages from the processor 5504 to applications installedon the host device and/or a remote device. As another example, one ormore of the interfaces 5510, 5512, 5514 may be adapted to allow a useror user device (e.g., personal computer (PC), etc.) tointeract/communicate with the processing system 5500. The processingsystem 5500 may include additional components not depicted in FIG. 55,such as long term storage (e.g., non-volatile memory, etc.).

In some embodiments, the processing system 5500 is included in a networkdevice that is accessing, or part otherwise of, a telecommunicationsnetwork. In one example, the processing system 5500 is in a network-sidedevice in a wireless or wireline telecommunications network, such as abase station, a relay station, a scheduler, a controller, a gateway, arouter, an applications server, or any other device in thetelecommunications network. In other embodiments, the processing system5500 is in a user-side device accessing a wireless or wirelinetelecommunications network, such as a mobile station, a user equipment(UE), a personal computer (PC), a tablet, a wearable communicationsdevice (e.g., a smartwatch, etc.), or any other device adapted to accessa telecommunications network.

In some embodiments, one or more of the interfaces 5510, 5512, 5514connects the processing system 5500 to a transceiver adapted to transmitand receive signaling over the telecommunications network. FIG. 56illustrates a block diagram of a transceiver 5600 adapted to transmitand receive signaling over a telecommunications network. The transceiver5600 may be installed in a host device. As shown, the transceiver 5600comprises a network-side interface 5602, a coupler 5604, a transmitter5606, a receiver 5608, a signal processor 5610, and a device-sideinterface 5612. The network-side interface 5602 may include anycomponent or collection of components adapted to transmit or receivesignaling over a wireless or wireline telecommunications network. Thecoupler 5604 may include any component or collection of componentsadapted to facilitate bi-directional communication over the network-sideinterface 5602. The transmitter 5606 may include any component orcollection of components (e.g., up-converter, power amplifier, etc.)adapted to convert a baseband signal into a modulated carrier signalsuitable for transmission over the network-side interface 5602. Thereceiver 5608 may include any component or collection of components(e.g., down-converter, low noise amplifier, etc.) adapted to convert acarrier signal received over the network-side interface 5602 into abaseband signal. The signal processor 5610 may include any component orcollection of components adapted to convert a baseband signal into adata signal suitable for communication over the device-side interface(s)5612, or vice-versa. The device-side interface(s) 5612 may include anycomponent or collection of components adapted to communicatedata-signals between the signal processor 5610 and components within thehost device (e.g., the processing system 5500, local area network (LAN)ports, etc.).

The transceiver 5600 may transmit and receive signaling over any type ofcommunications medium. In some embodiments, the transceiver 5600transmits and receives signaling over a wireless medium. For example,the transceiver 5600 may be a wireless transceiver adapted tocommunicate in accordance with a wireless telecommunications protocol,such as a cellular protocol (e.g., long-term evolution (LTE), etc.), awireless local area network (WLAN) protocol (e.g., Wi-Fi, etc.), or anyother type of wireless protocol (e.g., Bluetooth, near fieldcommunication (NFC), etc.). In such embodiments, the network-sideinterface 5602 comprises one or more antenna/radiating elements. Forexample, the network-side interface 5602 may include a single antenna,multiple separate antennas, or a multi-antenna array configured formulti-layer communication, e.g., single input multiple output (SIMO),multiple input single output (MISO), multiple input multiple output(MIMO), etc. In other embodiments, the transceiver 5600 transmits andreceives signaling over a wireline medium, e.g., twisted-pair cable,coaxial cable, optical fiber, etc. Specific processing systems and/ortransceivers may utilize all of the components shown, or only a subsetof the components, and levels of integration may vary from device todevice.

The following references are incorporated by reference herein as ifreproduced in their entireties:

-   -   TS 36.211 v13.0.0 http://www.3gpp.org/dynareport/36211.htm    -   TS36.213 v13.01 http://www.3gpp.org/dynareport/36213.htm    -   TS36.331 v13.0.0 http://www.3gpp.org/dynareport/36331.htm    -   TS36.212 v13.1.0        http://www.3gpp.org/ftp//Specs/archive/36_series/36.212/36212-d10.zip    -   TS36.321 v13.0.0 http://www.3gpp.org/dynareport/36321.htm.

In accordance with a first embodiment, a method for reference signaltransmission is provided. In this embodiment, the method includesreceiving one or more downlink transmissions over a first set ofaggregated component carriers is provided. The UE is capable oftransmitting uplink signals over fewer than all component carriers inthe first set of aggregated component carriers at the same time. Themethod further includes transmitting sounding reference signal (SRS)symbols over different component carriers in the first set of aggregatedcomponent carriers during different time periods. An apparatus forperforming this method is also provided.

In one example of the first embodiment, the step of transmitting the SRSsymbols includes receiving a radio resource control (RRC) message from abase station prior to transmitting the one or more SRS symbols over afirst component carrier in the set of aggregate component carriers. TheRRC message specifies a periodic SRS configuration parameter fortransmitting the one or more SRS symbols over the first componentcarrier. In such an example, the step of transmitting the SRS symbolsfurther includes periodically transmitting the one or more SRS symbolsover the first component carrier during periodic intervals in a sequenceof periodic intervals according to the periodic SRS configurationparameter specified by the RRC message. The RRC message may specify aperiod between consecutive intervals in the sequence of periodicintervals. Alternatively, the RRC message may specify orthogonalfrequency division multiplexed (OFDM) or single-carrierfrequency-division multiple access (SC-FDMA) symbol locations in whichthe one or more SRS symbols are to be transmitted over the componentcarrier.

In another example of the first embodiment, the step of transmitting theSRS symbols over the different component carriers includes receiving adownlink control information (DCI) message from a base station prior totransmitting one or more SRS symbols over a first component carrier inthe set of aggregate component carriers. The DCI message specifying anSRS configuration parameter for transmitting the one or more SRS symbolsover the first component carrier. In such an example, the step oftransmitting the SRS symbols further includes aperiodically transmittingthe one or more SRS symbols over the first component carrier accordingto the SRS configuration parameter specified by the DCI message. In oneinstance of this example, the DCI message specifies a transmit powerlevel for the one or more SRS symbols. In the same or another instanceof this example, the DCI message triggers the aperiodic transmission ofthe one or more SRS symbols over the first component carrier. In any oneof the above instances, or in a separate instance, of this example, theDCI message is received over a second component carrier that isdifferent than the first component carrier, and reception of the DCImessage over the second component carrier triggers cross-carriertransmission of the one or more SRS symbols over the first componentcarrier. In any one of the above instances, or in a separate instance,of this example, the UE receives the DCI message on a primary componentcarrier of the UE, and the one or more SRS symbols are transmitted overa secondary component carrier of the UE. In any one of the aboveinstances, or in a separate instance, of this example, the UE receivesthe DCI message over a common search space of a physical downlinkcontrol channel (PDCCH) of the UE. In any one of the above instances, orin a separate instance, of this example, the DCI message has a DCIlength that is equal to that associated with DCI format zero.

In another example of the first embodiment, the method further comprisesreceiving a radio resource control (RRC) message from a base stationspecifying a downlink control information (DCI) message format forsignaling an SRS configuration parameter over a physical downlinkcontrol channel (PDCCH). In such an example, the step of transmittingthe SRS symbols comprises monitoring the PDCCH for a DCI message havingthe DCI message format specified by the RRC message, and transmittingone or more SRS symbols over a first component carrier, in the first setof aggregated component carriers, according to the SRS configurationparameter signaled by the DCI message having the DCI message formatspecified by the RRC message. In one instance of this example, the RRCmessage specifies a specific DCI message format for indicating an SRStransmit power level. In the same or another instance of this example,the RRC message specifies a specific DCI message format for triggeringan aperiodic SRS symbol transmission. In any one of the above instances,or in a separate instance, of this example, the RRC message specifies aspecific DCI message format for triggering cross-carrier transmission ofan SRS symbol.

In all instances of all examples of the first embodiment, or in aseparate example of the first embodiment, the method further includestransmitting an uplink control message indicating uplink carrieraggregation capabilities of the UE.

In another example of the first embodiment, the method further includesreceiving a downlink control signal specifying a dual connectivity cellgroup configuration constraint from a network controller. The dualconnectivity cell group configuration constraint both (i) prohibits theUE from switching from a source component carrier in the first set ofaggregated component carriers monitored by a first base station to atarget component carrier in a second set of aggregated componentcarriers monitored by a second base station during a set of time periodsand (ii) prohibits the UE from switching from a source component carrierin the second set of aggregated component carriers monitored by thesecond base station to a target component carrier in the first set ofaggregated component carriers monitored by the first base station duringthe set of time periods. In one instance of this example, the step oftransmitting the SRS symbols comprises transmitting, via a firsttransmission chain (TX chain) of the UE, at least a first SRS symbolover different component carriers within the first set of aggregatedcomponent carriers during different time periods in a set of time periodwithout using the first TX chain to transmit any SRS symbol overcomponent carriers in the second set of aggregated component carriersduring any period in the set of time periods, and transmitting, via asecond TX chain of the UE, at least a second SRS symbol over differentcomponent carriers within the second set of aggregated componentcarriers during different time periods in the set of time period withoutusing the second TX chain to transmit any SRS symbol over componentcarriers in the second set of aggregated component carriers during anyperiod in the set of time periods.

In another example of the first embodiment, the method further comprisesreceiving a higher-layer control signal from a network controller thatspecifies a periodic uplink SRS switching configuration that instructsthe UE to switch between component carriers in the first set ofaggregated component carriers according to a periodic interval. In thisexample, the step of transmitting the SRS symbols includes transmittingat least one SRS symbol over each component carrier in the set ofaggregated component carriers according to the periodic uplink SRSswitching configuration during a first set of time periods, receiving amedia access control (MAC) message from the network controller thatdeactivates at least one component carrier in the set of aggregatedcomponent carriers, and transmitting at least one SRS symbol over eachremaining component carriers in the set of aggregated component carriersaccording to the periodic uplink SRS switching configuration during asecond set of time periods without transmitting any SRS symbols over theat least one deactivated component carrier during the second set of timeperiods.

In another example of the first embodiment, the method further comprisesreceiving a single downlink control message and at least a first field.The single downlink control message including multiple SRS instructionsfor multiple UEs. The method further comprises identifying the locationof an SRS instruction for the UE, amongst the multiple SRS instructionsin the single downlink control message, based on a number of bitsindicated by the field. In one instance of this example, the first fieldis a field within the single downlink control message. In the same oranother instance of this example.

In any one of the above instances, or in a separate instance, of thisexample, the first field is received via higher layer signaling.

In any one of the above instances, or in a separate instance, of thisexample, the SRS instruction indicates a transmit power level to be usedwhen transmitting SRS symbols.

In any one of the above instances, or in a separate instance, of thisexample, the SRS instruction indicates a condition for triggering anaperiodic SRS symbol transmission.

In another example of the first embodiment, the one or more downlinktransmissions are transmitted by a single base station. In one instanceof this example, the one or more downlink transmissions include at leasta first downlink transmission over the first component carrier and asecond downlink transmission over the second component carrier. Thefirst downlink transmission and the second downlink transmission aretransmitted by the same or different base stations during a common timeperiod. In such an instance, the first downlink transmission maycorrespond to a primary cell, and the second downlink transmission maycorrespond to a secondary cell. Alternatively, in such an instance, thefirst downlink transmission may correspond to a different secondary cellthan the second downlink transmission.

In accordance with a second embodiment, a method for reference signalreception is provided. In this embodiment, the method includestransmitting one or more downlink signals to a user equipment (UE) overa first set of aggregated component carriers. The UE is incapable oftransmitting uplink signals over all component carriers in the first setof aggregated component carriers at the same time. The method furtherincludes receiving sounding reference signal (SRS) symbols from the UEover different component carriers in a first set of aggregated componentcarriers during different time periods. An apparatus for performing thismethod is also provided.

In one example of the second embodiment, the RRC message specifies aperiod between consecutive intervals in the sequence of periodicintervals.

In the same or another example of the second embodiment, the RRC messagespecifies which orthogonal frequency division multiplexed (OFDM) orsingle-carrier frequency-division multiple access (SC-FDMA) symbollocations in which the one or more SRS symbols are to be transmittedover the component carrier.

In another example of the second embodiment, the method further includestransmitting a downlink control information (DCI) message to the UE thatspecifies an SRS configuration parameter for transmitting one or moreSRS symbols over a first component carrier, and receiving an SRS symbolfrom the UE over a first component carrier during a first period. TheSRS symbol was transmitted according to the SRS configuration parameterspecified by the DCI message. In one instance of this example, the DCImessage specifies a transmit power level for the SRS symbol. In anotherinstance of this example, the DCI message specifies an aperiodictransmission of the SRS symbol. In any one of the above instances, or ina separate instance, of this example the DCI message is received over asecond component carrier that is different than the first componentcarrier, and reception of the DCI message over the second componentcarrier triggers cross-carrier transmission of the SRS symbol over thefirst component carrier.

In another example of the second embodiment, the method further includestransmitting a radio resource control (RRC) message to the UE thatspecifies a downlink control information (DCI) format for indicating ansounding reference signal (SRS) configuration parameter, transmitting aDCI message having the DCI format to the UE, and receiving an SRS symbolfrom the UE after transmitting the DCI message having the DCI format tothe UE, where the DCI message instructed the UE to transmit the SRSsymbol according to the SRS configuration parameter. In such aninstance, the RRC message specifies a specific DCI message format forindicating an SRS transmit power level, a specific DCI message formatfor triggering an aperiodic SRS symbol transmission, and/or a specificDCI message format for triggering cross-carrier transmission of an SRSsymbol.

In another example of the second embodiment, the method furthercomprises receiving an uplink control message from the UE that indicatesuplink carrier aggregation capabilities of the UE, assigning an uplinkcarrier switching configuration to the UE based on the carrieraggregation capabilities of the UE, and sending a downlink controlsignal to the UE instructing the UE to transmit the SRS symbols over aset of aggregated component carriers based on the uplink carrierswitching configuration. In one instance of this example, the uplinkcarrier switching configuration specifies at least a first componentcarrier assigned to carry SRS symbol and physical uplink controlchannel/physical uplink shared channel (PUCCH/PUSCH) transmissions ofthe UE, and at least a second component carrier assigned to carrysounding reference signal (SRS) symbol transmissions of the UE withoutcarrying PUCCH/PUSCH transmissions of the UE. In such an instance, theuplink carrier switching configuration may instruct the UE to transmitat least one of a first SRS symbol and a PUSCH or PUCCH signal over thefirst component carrier during an initial period and a second SRS symbolover the second component carrier during a subsequent period followingthe initial period. In another instance of this example, the uplinkcarrier switching configuration specifies a periodic interval forswitching from a source component carrier to a target component carrier.

In another example of the second embodiment, the method furthercomprises transmitting a downlink control signal specifying a dualconnectivity cell group configuration constraint to the UE. The firstset of aggregated component carriers includes at least a first set ofaggregated component carriers monitored by a first base station and asecond set of aggregated component carriers monitored by a second basestation, and wherein the dual connectivity cell group configurationconstraint both (i) prohibits the UE from switching from a sourcecomponent carrier in the first set of aggregated component carriers to atarget component carrier in the second set of aggregated componentcarriers during a set of time periods and (ii) prohibits the UE fromswitching from a source component carrier in the second set ofaggregated component carriers to a target component carrier in thesecond set of aggregated component carriers during the set of timeperiods.

In another example of the second embodiment, the method further includesreceiving an uplink control message from the UE. The uplink controlmessage includes two or more bits indicating an uplink radio frequency(RF) retuning delay of the UE for switching from a source componentcarrier to a target component carrier, as well as a single bit that isset to either a first value to indicate that a downlink retuning delayof the UE is equal to the uplink retuning delay of the UE or a secondvalue when the downlink retuning delay of the UE is equal to zero. Inthis example, the method further includes assigning an uplink carrierswitching configuration to the UE based on the downlink retuning delayof the UE, and sending a downlink control signal to the UE thatinstructs the UE to transmit the SRS symbols over a first set ofaggregated component carriers based on the uplink carrier switchingconfiguration. In one instance of this example, the uplink controlmessage indicates a specific uplink retuning delay for switching from afirst RF band containing the source component carrier to a second RFband containing the target component carrier. In such an instance, thefirst RF band may be different than the second RF band and/or the two ormore bits of the uplink control message may indicate the uplink RFretuning delay of the UE as a number of orthogonal frequency divisionmultiplexed (OFDM) or single-carrier frequency-division multiple access(SC-FDMA) symbols.

In another example of the second embodiment, the method further includestransmitting, by the base station, a single downlink control message toboth a first UE and a second UE, a first field to the first UE, and asecond field to the second UE. The single downlink control messagecarries a first SRS instruction for the first UE and a second SRSinstruction for the second UE. The first field indicates a number ofbits used to indicate the first SRS instruction in the single downlinkcontrol message, and the second field indicates a number of bits used toindicate the second SRS instruction in the single downlink controlmessage. In one instance of this example, the first field and the secondfield are fields within the single downlink control message. In anotherinstance of this example, the first field and the second field aretransmitted to the first UE and the second UE, respectively, via higherlayer signaling. In any one of the above instances, or in a separateinstance, of this example, the first SRS instruction and the second SRSinstruction indicate transmit power levels to be used by the first UEand the second UE, respectively, when transmitting SRS symbols and/orthe first SRS instruction and the second SRS instruction indicate SRStriggering conditions for triggering SRS symbol transmissions by thefirst UE and the second UE, respectively.

In accordance with a third embodiment, a method for transmitting uplinksignals is provided. In this embodiment, the method includestransmitting a first uplink signal in a first subframe over a firstcomponent carrier during a first period. The first uplink signalcarrying at least a first sounding reference signal (SRS) symbol. Themethod further includes switching from the first component carrier to asecond component carrier according to an SRS switching schedule. Anuplink RF retuning delay is associated with switching from the firstcomponent carrier to the second component carrier. The method furtherincludes transmitting a second uplink signal in a second subframe overthe second component carrier during a second period. The second uplinksignal carries at least one of a second SRS symbol and a random accesspreamble.

In one example of the third embodiment, the method further includessending, by the UE, an uplink control message to a base station thatspecifies a duration of the uplink RF retuning delay. In one instance ofthis example, the uplink control message includes two or more bitsindicating the duration of the RF retuning delay of the UE and a singlebit being set to either a first value to indicate that a downlink RFretuning delay of the UE is equal to the uplink RF retuning delay of theUE or a second value to indicate that the downlink RF retuning delay ofthe UE is equal to zero. In another instance of this example, the two ormore bits of the uplink control message indicate the uplink RF retuningdelay of the UE as a number of orthogonal frequency division multiplexed(OFDM) or single-carrier frequency-division multiple access (SC-FDMA)symbols. In such an instance, the UE may not monitor or receive physicaldownlink control channel (PDCCH) or physical downlink shared channel(PDSCH) over orthogonal frequency division multiplexed (OFDM) orsingle-carrier frequency-division multiple access (SC-FDMA) symbols ofthe second component carrier that overlap in time with the downlink RFretuning delay.

In another example of the third embodiment, transmitting the seconduplink signal in the second subframe over the second component carrierduring the second period comprises puncturing a portion of the seconduplink signal corresponding to a duration of the uplink RF retuningdelay.

In accordance with a fourth embodiment, a method for reference signalswitching is provided. In this embodiment, the method includestransmitting a first sounding reference signal (SRS) symbol over aprimary component carrier during a first period. The UE that transmittedthe SRS symbol is scheduled to transmit both a second SRS symbol over asecondary component carrier during a second period and an uplink controlmessage over the primary carrier during the second period. This createsa scheduling conflict between the SRS symbol and the uplink controlmessage. The method further includes transmitting the uplink controlmessage over the primary component carrier during the second periodwithout transmitting the second SRS symbol over the secondary componentcarrier during the second period when the uplink control messagesatisfies a criterion.

In one example of the fourth embodiment, the uplink control messagesatisfies the criterion when the uplink control message includes anacknowledgement or negative acknowledgement (ACK/NACK) message. In oneinstance of such an example, the uplink control message satisfies thecriterion when the uplink control message includes channel stateinformation (CSI).

In any one of the above instances, or in a separate instance, of thisexample, or in another example entirely, the method further comprisestransmitting the second SRS symbol over the secondary carrier during athird period following the second period. The third period may be thenext available opportunity for transmitting the second SRS symbol.

In accordance with a fifth embodiment, a method for transmitting uplinksignals is provided. In this embodiment, the method includes receiving acontrol signal from a base station that indicates that a set ofaggregated component carriers are assigned to a timing advance group(TAG). At least a first component carrier assigned to the TAG does notsupport physical uplink control channel (PUCCH) signaling or physicaluplink shared channel (PUSCH) signaling. The method further includestransmitting a sounding reference signal (SRS) symbol over one or morecomponent carriers assigned to the TAG according to a timing advanceparameter associated with the TAG.

In one example of the fifth embodiment, the method further comprisestransmitting a random access preamble to a base station to request atiming advance for the first component carrier, receiving a controlsignal from the base station that indicates the timing advance for thefirst component carrier, and transmitting a first sounding referencesignal (SRS) symbol over the first component carrier during a firstperiod in accordance with the timing advance without transmitting anyPUSCH signaling and without transmitting any PUCCH signaling over thefirst component carrier during the first period. In one instance of suchan example, the method further includes transmitting a second SRS symbolover a second component carrier during a second period. In such aninstance, the UE transmits the first SRS symbol over a first componentcarrier during the first period without transmitting any uplinksignaling over a second component carrier during the first period, andtransmits the second SRS symbol over the second component carrier duringthe second period without transmitting any uplink signaling over thefirst component carrier during the second period. In such an instancethe UE may transmit the second SRS symbol over the second componentcarrier during the second period based on a preconfigured SRS switchinginterval without receiving explicit instructions to switch from thefirst component carrier to the second component carrier, in which casethe preconfigured SRS switching interval may be a periodic switchinginterval that requires the UE to transmit SRS symbols over differentsubsets of component carriers in the set of aggregated componentcarriers during different time periods in a series of periodicallyoccurring time periods. In any one of the above instances, or in aseparate instance, of this example the method further comprisesreceiving a switching instruction from a base station that instructs theUE to transmit the second SRS symbol over the second component carrierduring the second period. The switching instruction may have beenreceived in a downlink control information (DCI) message.

In accordance with a sixth embodiment, a method for receiving uplinksignals is provided. In this embodiment, the method includestransmitting a downlink signal to a UE over a set of aggregatedcomponent carriers, receiving a first sounding reference signal (SRS)symbol from the UE over a first component carrier in the set ofaggregated component carriers during a first period, and receiving asecond SRS symbol from the UE over a second component carrier in the setof aggregated component carriers during a second period. The secondcomponent carrier is different than the first component carrier.

In one example of the sixth embodiment, the first SRS symbol is receivedfrom the UE over the first component carrier during the first periodwithout receiving any uplink signaling from the UE over the secondcomponent carrier during the first period, and the second SRS symbol isreceived from the UE over the second component carrier during the secondperiod without receiving any uplink signaling from the UE over the firstcomponent carrier during the second period.

In that example, or another example, of the sixth embodiment, the methodfurther includes transmitting a switching instruction to the UE thatinstructs the UE to transmit the second SRS symbol over the secondcomponent carrier during the second period.

In any of the above examples, or in another example, of the sixthembodiment, the first component carrier supports physical uplink sharedchannel (PUSCH) transmissions. In such an example, the second componentcarrier may not support PUSCH transmissions.

In any of the above examples, or in another example, of the sixthembodiment the method further includes transmitting at least one of athird SRS symbol, PUSCH, and PUCCH over the first component carrierduring a third period unless the UE has been instructed to transmit thethird SRS symbol over a different component carrier that does notsupport PUSCH and/or PUCCH transmissions.

In any of the above examples, or in another example, of the sixthembodiment, the first component carrier is frequency division duplexed(FDD) and the second component carrier is time division duplexed (TDD)or in an unpaired spectrum. Alternatively, the first component carrierand the second component carrier may be time division duplexed (TDD) orin an unpaired spectrum.

In any of the above examples, or in another example, of the sixthembodiment, the method further includes receiving a first downlinktransmission over the first component carrier and a second downlinktransmission over the second component carrier, where transmissionparameters for the first downlink transmission are derived from receivedsignal information corresponding to the first SRS symbol, andtransmission parameters for the second downlink transmission are derivedfrom received signal information corresponding to the second SRS symbol.

In any of the above examples, or in another example, of the sixthembodiment, the UE transmits the SRS configuration parameter over thefirst component carrier during the first period without transmitting anyphysical uplink shared channel (PUSCH) signaling over the firstcomponent carrier during the first period and without transmitting anyphysical uplink control channel (PUCCH) signaling over the firstcomponent carrier during the first period.

In accordance with a seventh embodiment, a method for transmittingcontrol signals is provided. In this embodiment, the method includestransmitting a control signal to a UE. The control signal indicates thata set of aggregated component carriers are assigned to a timing advancegroup (TAG). At least one component carrier assigned to the TAG does notsupport physical uplink control channel (PUCCH) signaling and physicaluplink shared channel (PUSCH) signaling, and the control signal promptsthe UE to transmit a sounding reference signal (SRS) symbol over one ormore component carriers assigned to the TAG according to a timingadvance parameter associated with the TAG.

In accordance with a seventh embodiment, a method for transmittingcontrol signals is provided. In this embodiment, the method includestransmitting a control signal to a UE. The control signal indicates thata set of aggregated component carriers are assigned to a timing advancegroup (TAG). At least one component carrier assigned to the TAG does notsupport physical uplink control channel (PUCCH) signaling and physicaluplink shared channel (PUSCH) signaling, and the control signal promptsthe UE to transmit a sounding reference signal (SRS) symbol over one ormore component carriers assigned to the TAG according to a timingadvance parameter associated with the TAG.

In one example of the seventh embodiment, the control signal is adownlink control information (DCI) message.

In another example of the seventh embodiment, the method furtherincludes receiving at least one of a random access channel (RACH)message and an SRS symbol over a secondary component carrier that doesnot carry PUCCH or PUSCH transmissions of the UE.

In one instance of this example, the RACH message is transmitted over anon-contention based access channel. In such an instance, the RACHmessage and the SRS symbol may be received over the secondary componentcarrier. In another instance of this example, the method furtherincludes receiving a PUCCH or PUSCH transmission from the UE over aprimary component carrier prior to receiving the RACH message and/or theSRS symbol over the secondary component carrier. In such an instance,the UE switches from the primary component carrier to the secondarycomponent carrier after sending the PUCCH or PUSCH transmission over theprimary component carrier. In such an instance, the method may furtherinclude transmitting a downlink control instruction (DCI) message to theUE that instructs the UE to switch from the primary component carrier tothe secondary component carrier.

In accordance with an eighth embodiment, a method for receiving uplinksignals is provided. In this embodiment, the method includes receiving arandom access channel (RACH) transmission from a user equipment (UE).The RACH transmission requests a timing advance for a component carrierwithout requesting a grant for physical uplink control channel (PUCCH)resource and without requesting a grant for physical uplink sharedchannel (PUSCH) resources. The method further includes transmitting acontrol signal to the UE that indicates the timing advance for thecomponent carrier, and receiving one or more sounding reference signal(SRS) symbols from the UE over the component carrier in accordance withthe timing advance without receiving any PUSCH signaling over thecomponent carrier and without receiving any PUCCH signaling over thecomponent carrier.

In accordance with a ninth embodiment, a method for reference signaltransmission is provided in this embodiment, the method includesreporting a component carrier capability of a user equipment (UE) to abase station, configuring the UE based on information from the basestation, a first set of component carriers for one or more downlinkreception, configuring the UE based on information from the base stationa first subset of component carriers, in the first set of componentcarriers, for one or more uplink transmissions. The one or moretransmissions include at least one of physical uplink control channel(PUCCH), physical uplink shared channel (PUSCH), or sounding referencesignal (SRS) symbol transmissions. The UE is capable of transmittinguplink signals over all component carriers in the first subset ofcomponent carriers at the same time. The method further includesconfiguring the UE based on information from the eNB, a second subset ofcomponent carriers, in the first set of component carriers, for one ormore SRS transmissions without configured the second subset of componentcarriers for PUSCH/PUCCH transmissions, and transmitting SRS symbolsover different component carriers in the first subset of componentcarriers and second subset of component carriers during different timeperiods.

In one example of the ninth embodiment, the number of component carriersin the first subset of component carriers and the second subset ofcomponent carriers exceeds the UE's indicated uplink carrier aggregationcapability. In the same or different instance of this example, thenumber of component carriers in the second subset of component carriersexceeds the UE's indicated uplink carrier aggregation capability.

In accordance with a tenth embodiment, a method for reference signaltransmission is provided. In this embodiment, the method includestransmitting a first uplink signal over a first component carrier duringa first period. The first uplink signal carries at least a firstsounding reference signal (SRS) symbol. The method further includesswitching from the first component carrier to a second component carrieraccording to a switching parameter for an SRS switching schedule, andtransmitting a second uplink signal over the second component carrierduring a second period. The second uplink signal carrying at least oneof a second SRS symbol and a random access preamble, wherein thetransmission occurs after an uplink RF retuning time.

In one example of the tenth embodiment, the switching parameter isdetermined by a configuration received prior to the first period.

In another example of the tenth embodiment, the switching parameter isdetermined by a messaging received during the first period.

In accordance with an eleventh embodiment, a method for reference signaltransmission is provided. The method comprises receiving one or moredownlink transmissions over a set of aggregated component carriers, andtransmitting at least one of a first sounding reference signal (SRS)symbol, and at least one of physical uplink shared channel (PUSCH)signal and physical uplink control channel (PUCCH) signaling over afirst component carrier in the set of aggregated component carriersduring a first period. At least one of the parameters for the SRS symbolis generated based on a parameter for the PUSCH. The method furtherincludes transmitting at least a second SRS symbol over a secondcomponent carrier in the set of aggregated component carriers during asecond period without transmitting any PUSCH signal and PUCCH signalingover the second component carrier during the second period. The secondcomponent carrier being different than the first component carrier, andnone of the parameters for the SRS symbol is generated based on aparameter for any PUSCH.

In one example of the eleventh embodiment, the method further comprisesreceiving a control signal from a base station that indicates that thesecond component carrier is assigned to a timing advance group (TAG),and transmitting a sounding reference signal (SRS) symbol over one ormore component carriers assigned to the TAG according to a timingadvance parameter associated with the TAG.

Although the description has been described in detail, it should beunderstood that various changes, substitutions and alterations can bemade without departing from the spirit and scope of this disclosure asdefined by the appended claims. Moreover, the scope of the disclosure isnot intended to be limited to the particular embodiments describedherein, as one of ordinary skill in the art will readily appreciate fromthis disclosure that processes, machines, manufacture, compositions ofmatter, means, methods, or steps, presently existing or later to bedeveloped, may perform substantially the same function or achievesubstantially the same result as the corresponding embodiments describedherein. Accordingly, the appended claims are intended to include withintheir scope such processes, machines, manufacture, compositions ofmatter, means, methods, or steps.

What is claimed is:
 1. A method comprising: transmitting, by a userequipment (UE), a first uplink transmission over a first carrier of awireless network during a first period, the first uplink transmissioncarrying at least one of a first sounding reference signal (SRS), aphysical uplink shared channel (PUSCH), or a physical uplink controlchannel (PUCCH); switching, by the UE, from the first carrier to asecond carrier, a time duration for the switching being related to aradio frequency (RF) retuning time of the UE, and the RF retuning timebeing based on a capability of RF retuning of the UE for switchingbetween the first carrier and the second carrier; and transmitting, bythe UE, a second uplink transmission over the second carrier during asecond period, the second uplink transmission carrying at least one of asecond SRS and a random access preamble, wherein the UE is configuredwith the first carrier and the second carrier.
 2. The method of claim 1,wherein the UE interrupts monitoring or receiving physical downlinkcontrol channel (PDCCH) or physical downlink shared channel (PDSCH) overorthogonal frequency division multiplexed (OFDM) symbols of the firstcarrier that overlap in time with the RF retuning time.
 3. The method ofclaim 1, wherein the first carrier and the second carrier are in samefrequency band.
 4. The method of claim 1, wherein the first carrier andthe second carrier are in different frequency bands.
 5. The method ofclaim 1, wherein the UE temporarily suspends transmitting uplink signalsover orthogonal frequency division multiplexed (OFDM) or single-carrierfrequency-division multiple access (SC-FDMA) symbols of the firstcarrier that overlap in time with the RF retuning time.
 6. The method ofclaim 1, further comprising: sending, by the UE, a higher layersignaling message indicating the RF retuning time to a base station ofthe wireless network, the higher layer signaling message specifying aduration of the RF retuning time.
 7. The method of claim 6, wherein thehigher layer signaling message includes two or more bits indicating theduration of the RF retuning time.
 8. The method of claim 7, wherein thetwo or more bits of the higher layer signaling message indicate the RFretuning time of the UE as a number of orthogonal frequency divisionmultiplexed (OFDM) or single-carrier frequency-division multiple access(SC-FDMA) symbols.
 9. The method of claim 7, wherein the two or morebits of the higher layer signaling message indicate the duration of theRF retuning time in microseconds.
 10. A user equipment (UE) comprising:a processor; and a non-transitory computer readable storage mediumstoring programming for execution by the processor, the programmingincluding instructions to: transmit a first uplink transmission over afirst carrier of a wireless network during a first period, the firstuplink transmission carrying at least one of a first sounding referencesignal (SRS), a physical uplink shared channel (PUSCH), or a physicaluplink control channel (PUCCH); switch from the first carrier to asecond carrier, a time duration for the switching being related to aradio frequency (RF) retuning time, and the RF retuning time being basedon a capability of RF retuning of the UE for switching between the firstcarrier and the second carrier; and transmit a second uplinktransmission over the second carrier during a second period, the seconduplink transmission carrying at least one of a second SRS and a randomaccess preamble, wherein the UE is configured with the first carrier andthe second carrier.
 11. The UE of claim 10, wherein the UE interruptsmonitoring or receiving physical downlink control channel (PDCCH) orphysical downlink shared channel (PDSCH) over orthogonal frequencydivision multiplexed (OFDM) symbols of the first carrier that overlap intime with the RF retuning time.
 12. The UE of claim 10, wherein the UEtemporarily suspends transmitting uplink signals over orthogonalfrequency division multiplexed (OFDM) or single-carrierfrequency-division multiple access (SC-FDMA) symbols of the firstcarrier that overlap in time with the RF retuning time.
 13. The UE ofclaim 10, wherein the first carrier and the second carrier are in samefrequency band.
 14. The UE of claim 10, wherein the first carrier andthe second carrier are in different frequency bands.
 15. The UE of claim10, wherein the programming further includes instructions to: send ahigher layer signaling message indicating the RF retuning time to a basestation of the wireless network, the higher layer signaling messagespecifying a duration of the RF retuning time.
 16. The UE of claim 15,wherein the higher layer signaling message includes two or more bitsindicating the duration of the RF retuning time.
 17. The UE of claim 16,wherein the two or more bits of the higher layer signaling messageindicate the duration of the RF retuning time in microseconds.
 18. TheUE of claim 16, wherein the two or more bits of the higher layersignaling message indicate the RF retuning time of the UE as a number oforthogonal frequency division multiplexed (OFDM) or single-carrierfrequency-division multiple access (SC-FDMA) symbols.